Concl: wasps lay exactly the number of eggs.....in host's, suitable egg.
Premise 1: if more these eggs will die due to cause 1
Premise 2: if fewer then eggs are still destroyed due to cause 2
What does the passage suggest? or concl the passage supports?
Here it is asked of us to repeat what the passage said in other words.
A) obviously, in case of suitable egg, Wasp is successful there fore it must have known the numbers of eggs it would lay in the hosts exactly. - lets keep this contender... as the passage says it does...even if the answer had said largest, this would still be contender as the passage used 'exact' to describe the situation.
B) host insects lack defense -- out of scope, we are talking about larvae here
C) wasp knows how many eggs to lay in a host by experience - we know if know the lay the exact number but no where we are told that this is caused by experience
D) failure to lay enough eggs will be detremental to wasp - well though cause 2 accounts for this, the relative speed between laying and destroying is not suggested.
E)wasp knows how many eggs to lay using visual cues - same as C, we know the part 1 of the sentence occurs but we are not told that its visual cues guide it.
So A is the only option, though D is attractive.
Hope this helps