After determining the levels of calcium carbonate

[Venkat]

Source: GMAT Prep - Take 2

After determining the levels of calcium carbonate and the types of fossilized algae present in the core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able to reconstruct the history of precipitation in tropical South America over the past 25,000 years.

(A) the types of fossilized algae present in the core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able
(B) the types of fossilized algae that are present in core samples taken from the bottom of Lake Titicaca in The Andes, it was possible for a group of scientists
(C) the types of fossilized algae that had been present in core samples taken from the bottom of Lake Titicaca in The Andes, that made it possible for a group of scientists
(D) what types of fossilized algae had been present in core samples taken from the bottom of Lake Titicaca in The Andes, it was possible for a group of scientists
(E) what the types of fossilized algae were that were present in core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able

I was able to eliminate the choices D and E, because they exhibit poor parallelism ( 'the levels' versus 'what the types' )
Also, C is incorrect because of the incorrect tense 'had been'
Can someone explain the choices A and B and the corresponding concepts/rules involved?

Is B wrong because 'it' does not have a clear antecedent?

[RonPurewal]

Source: GMAT Prep - Take 2

After determining the levels of calcium carbonate and the types of fossilized algae present in the core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able to reconstruct the history of precipitation in tropical South America over the past 25,000 years.

(A) the types of fossilized algae present in the core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able
(B) the types of fossilized algae that are present in core samples taken from the bottom of Lake Titicaca in The Andes, it was possible for a group of scientists
(C) the types of fossilized algae that had been present in core samples taken from the bottom of Lake Titicaca in The Andes, that made it possible for a group of scientists
(D) what types of fossilized algae had been present in core samples taken from the bottom of Lake Titicaca in The Andes, it was possible for a group of scientists
(E) what the types of fossilized algae were that were present in core samples taken from the bottom of Lake Titicaca in The Andes, a group of scientists was able

I was able to eliminate the choices D and E, because they exhibit poor parallelism ( 'the levels' versus 'what the types' )
Also, C is incorrect because of the incorrect tense 'had been'
Can someone explain the choices A and B and the corresponding concepts/rules involved?

Is B wrong because 'it' does not have a clear antecedent?

there's a really important concept at work here: the subjectless initial modifier. the rule for initial modifiers that don't have subjects is simple: such modifiers are automatically attributed to the IMMEDIATELY FOLLOWING noun/pronoun.

here's my favorite example:
coming home from school, the wind blew me off my bike.
wrong.
according to this sentence, the wind was coming home from school.
2 ways you could fix this:
(a) change the immediately following (pro)noun: coming home from school, i was blown off my bike by the wind. --> notice that this constitutes a perfectly acceptable use of the passive voice
(b) insert a subject and verb into the modifier: as i was coming home from school, the wind blew me off my bike.

choice (b) has the same problem: according to that choice, the mysterious "it", rather than the scientists, determined the levels of CaCO3 and the types of algae present in the lake.
by contrast, choice (a) correctly attributes the modifier to "a group of scientists".

[jessie-cn2007]

Hi Ron,
I notice the suspicious "present" in choice A. I believe the Verb "present" is inappropriate here, thus A is wrong.
Before you make a comment, I would give myself a slating for doubting the official answer.

[RonPurewal]

Hi Ron,
I notice the suspicious "present" in choice A. I believe the Verb "present" is inappropriate here, thus A is wrong.
Before you make a comment, I would give myself a slating for doubting the official answer.

if "present" were indeed a verb, it would most certainly be wrong. however, it's not a verb; it's an adjective style modifier.
it has the same usage as it does in the following simpler sentence: only 20 of the 100 students were present at the assembly.

[tina_2c]

a group of scientists was vs a group of scientists were--
doesnt the above sub-verb agreement depend on the of preposition.
"a group was"- correct
"a group of scientists were"..........??? help me

[RonPurewal]

a group of scientists was vs a group of scientists were--
doesnt the above sub-verb agreement depend on the of preposition.
"a group was"- correct
"a group of scientists were"..........??? help me

full disclosure:
the full explanation is that these sorts of collective nouns can actually be either singular or plural, depending on the emphasis of the sentence.
if the sentence emphasizes the collective action of the group, then the verb should correspondingly be singular; if the sentence emphasizes the individual actions of the different members of the group, then the verb should correspondingly be plural.
for instance:
the faculty is going to meet to discuss the proposal (since the faculty does this all at the same time, all at once)
BUT
the faculty go home to their houses after the day is over (you wouldn't put this in the singular unless the entire faculty lives in the same house!)

that said, i think it is EXTREMELY unlikely that you'll ever be tested on this sort of difference, so i don't think it's terribly worth worrying about.