From 1965 on, region’s standard of living has soared

[RichaChampion]

Mr. Purewal I had no issue in picking up "but" because intuitively i know that contrast is needed, but I think "so" is a connector of cause and effect.

But I am unable to understand the correct usage of so in Option C. The Cause and effect part is correct, but this one seems in doldrums -

When "so" connects two ideas"” i.e., idea #2 is a consequence of idea #1"”you need to have complete sentences before AND after "so".
(Complete Sentence) + So + (Other Complete Sentence)

Reference Link

I mean the part after so doesn't seems to be a complete sentence here or I am missing something? Or the subject is implied here (Ellipsis) -

but so have = but so (the region’s) have

[RonPurewal]

this sentence has nothing to do with cause and effect.
(clearly -- just think about the fact that there's a contrast between the two parts!)

this is a different kind of "so".
basically, it means "the same thing i said earlier applies here, too". it's the same "so" that appears in constructions like "do so".

e.g., the following are correct sentences (whose meanings should be perfectly clear):

Students who have completed all three introductory physics courses are automatically eligible for the intermediate physics course. Students who have not done so cannot take the intermediate course without permission from the instructor.
("done so" = "completed all three introductory physics courses")

Engineers' salaries are much higher in California than in the Midwest, but so are the cost of housing and the cost of living in general.
("so are..." = "are much higher, too")

[aflaamM589]

Hello Ron,
Why is A incorrect.
I understand the difference between C and E: Time frame is not changing so remain in same tense. perfect!

But why not drop verb (have) altogether?
Is also with but incorrect?
I understand and also is a thing.
Is but also not a thing/ illogical?
Thank you very much
Have a nice day

[RonPurewal]

Hello Ron,
Why is A incorrect.

A ends with "but also" + nouns.
to create proper parallelism, that would have to be preceded by another noun... but it isn't.

But why not drop verb (have) altogether?

"so" is an adverb. without a verb there, you can't use "so".

[aflaamM589]

Perfect!
the explanation made my day.
Thank you very much

[RonPurewal]

you're welcome.