The Bends problem

[sushant.bhola]

Because of differences in the human body's internal pressure and the ocean's, it is essential that a diver returning to the surface ascends slowly or they will suffer a painful condition known as the "bends."

a) differences in the human body's internal pressure and the ocean's, it is essential that a diver returning to the surface ascends slowly or they

b) the difference between the human body's internal pressure and the ocean's, it is essential that a diver returning to the surface ascend slowly or they

c) the difference in the human body's internal pressure and that of the ocean, it is essential that a diver returning to the surface ascends slowly or he

d) differences in the human body's internal pressure and that of the ocean, it is essential that a diver returning to the surface ascend slowly or they

e) the difference between the internal pressure of the human body and that of the ocean, it is essential that a diver returning to the surface ascend slowly or he

Correct Answer is E.
In above question why does correct answer use ascend instead of 'ascends'. According to me both verbs in below sentence fragment must be singular.
'diver ..... ascends or he will suffer.......)

Could you please explain what am I missing here?

[RonPurewal]

Try googling (or looking up in the MGMAT materials) "command subjunctive". That will explain it.

I think the MGMAT materials also refer to the same concept as "Bossy Verbs", or something similar.

[sushant.bhola]

Got what I was missing, Thanks

[RonPurewal]

You're welcome.

[MADHURIG370]

I am confused between the use of ascend and ascends. Please explain.

[Sage Pearce-Higgins]

They are both part of the verb 'to ascend'. The infinitive (base form of the verb) is 'ascend', and we'd say 'a diver ascends' if we're using the present tense. However, in certain constructions we'd use the infinitive (i.e. just 'ascend'). That's what's happening here: 'it is essential that he [infinitive]'. This probably sounds a weird, as it's a bit more formal and old-fashioned than our usual way of speaking. However, you're likely to see such constructions on GMAT. If I work with a student individually, I recommend that she become familiar with this part of grammar, called the 'command subjunctive'. Take a look in the SC strategy guide chapter 12 for more on this.