First off, try this tricky antonym problem.
Before I get to the answer, this problem (perhaps not so transparently) is meant to highlight the word recondite. Maybe you even chose this as the answer. Recondite, however, is not correct. Let’s see why.
The GRE favors words that students are apt to confuse. One of the reasons a word is confusing is you mix it up with a word that looks or sounds similar. Another possibility is the word itself just doesn’t mean what you would expect it to mean. When this is the case, we often look at a part of a word and relate it to a word that is actually unrelated.
Recondite fits this latter category because students often think it relates to the word reckon. Reckon, however, means to consider or think of something as. (e.g., I reckon that if there are many gray clouds in the sky it is likely to rain.) Recondite, on the other hand, is an adjective and means difficult to understand or obscure/little known. For example:
Quantum physics is a recondite field because very few people really understand it.
So if you work off the assumption that the word is related to reckon (an inference many of us are prone to making) then you will actually think the meaning of the word is very different from what it actually is. For the antonym above you may know the meaning of inscrutable but think that to recondite relates to reckon, in which case you’ve been trapped.
The actual answer is (A). Inscrutable means difficult to fathom or comprehend. This word usually refers to motives. That is, if you have no idea what somebody is doing (they’re wearing a poker face) then they are inscrutable. If you know somebody’s motives then that person is transparent.
Anyways, I reckon that hopefully you will no longer confuse the word recondite with reckon. At least one easy way to not get mixed up is to remember that the word recondite is itself recondite. That is, very few people know the word recondite.