codesnooker wrote:

Somerandomguy wrote: My understanding is that you only negate "necessary assumption" questions, not inference questions. Please comment....

You are absolutely correct that we apply negation technique to Assumption questions. Also, IMO, this question comes under category of either "Must be true" or "interference" question.

Also both choices (A) and (D) are very strong contender of right choices. So irrespective of any special technique if we look at both the options then we can see that option (A) used the term USUALLY, which means it could be 50% or more but less then 100%. So that means we are not very sure about still pigeons are used for classified information transmission. That leads this option (A) into the DOUBT OF SCOPE.

On the other hand, we negate (If it is difficult to understand the scope of any statement then try to negate the statement to understand its scope) the choice (D) then, we can see that premises doesn't stand itself for the conclusion. Hence, (D) "must be true" in order to lead the conclusion.

So in IMO (D) should be the correct answer, irrespective of other choices.

Hope this helps...

codesnooker wrote: For more details, for example, lets say pigeons communication were first time recorded in the history books during 1810 A.D. So, it means that before 1810 A.D. the pigeons should be used during the warfare.

So this makes the (D) most strong contender among all the choices.

stubbornp wrote:OA D