the use of the word 'both' at the start of the sentence suggests at least two examples will be listed. c is the only answer that allows for a list to be created (in this case intelligent and artistic)
a) he is both intelligent and also artistic.
the word 'also' in this example suggests it's an add on the a previous list, when theres only one previous example (intelligent).
b) he is both intelligent as well as artistic.
same as the last choice, the 'as well as' suggests its another example following the previous list, instead of there being just one previous example.
c) he is both intelligent and artistic.
just the word 'and' shows its a continuation of the list that the reader is expecting, since the word 'both' is used at the start of the sentence.
d) he is both intelligent besides artistic.
as per answers a) and b), there is no list to continue on from the use of the word 'both'
