To grumpy: wow... that explained many things
Notice that G's evidence does NOT say that an equal number of works of each type were submitted. It says that an equal number of ARTISTS of each type submitted works (and that no artist submitted more than one type of work). His second piece of evidence is that more photographic WORKS were displayed than the other types. His conclusion is that there was "bias".
Key point I’ve missed: “each artist was allowed to submit one work” i.e. a sculptor could submit not a sculpture!
But let's stop and understand what that one-word conclusion really means. It actually means "the proportion of photographic WORKS displayed exceeded the proportion of PHOTOGRAPHERS because of a deliberate action by the organizers". In other words, this is a standard cause-and-effect conclusion, although well hidden. The conclusion is that the organizers' actions CAUSED the disproportionate number of photographs to be displayed.
Did not see organizers' fault here:
Info extracted from G's evidence: = # of Ph-s, Sc-s, Pa-s; each - only one work; More pics shown
G's conclusion: bias (organizers showed more pics maybe?)
H weakens this by saying that the organizers did NOT preferentially select photographs over other works; instead, every work submitted that met the criteria was displayed. Thus, he provides another cause for the difference, other than actions by the organizers. This other (proposed) cause is simply that more eligible photographic WORKS were submitted. Providing an alternative cause is, of course, the most common way of weakening a cause-and-effect argument.
H's evidence: all submited works were shown (thus not organizers fault)
didn't spot the cause-and-effect argument at first...
So in order to strengthen G again, we need a fact which says that the organizers' actions did cause, or could have caused, the disproportion. BUT this fact must be consistent with all the evidence that already exists! So we are NOT actually ignoring the evidence; we must fully recognize it and accept it. That is, we must find a fact which not only makes the organizers' actions a probable cause of the disproportion, but also does NOT contradict any of G's or H's evidence.
Clearly, only B does this.
This LSAT-type question would be somewhat rare on the GMAT. The GMAT usually makes cause-and-effect conclusions easier to see and understand than this one is.
tnx and kudos to you.