Assiduous : inattentive : : a. cordial : unsociable b. corporeal : incarnate c. dorsal : sedentary d. digital : technical e. sedentary : thoughtful

A. cordial : unsociable

When it comes to these types of questions, there are two basic things you’ll need to do.  The first is define the words.  Then, after you have mentally defined the words, the next step is to determine the relationship of the first two words--"assiduous” means nonstop/constant/relentless, and “inattentive” means not paying attention.  What this tells us is that the two words are antonyms because of they mean quite opposite things.  What that means is that when looking at the possible choices of answers, we’ll need to be on the lookout for antonyms as well. Here is an example of how things will look (note the antonym relation):

left : right :: up : down

With that in mind, because “cordial” means friendly/courteous (which is what one can be in a social setting), and “unsociable” means having an aversion to being friendly, we can see these two words are opposites (antonyms).  As such, the best response is “A.”