The correct option is
C The few
In the sentence, 'friends' is a plural countable noun.
Fewis a quantifier used with plural countable nouns.
Without the article, fewemphasizes a small number of something.
Adding the article removes the emphasis—a few means some.
It has a positive meaning.
The few means not many, but all of those. This has a bit negative meaning. The sentence implies this meaning.
In the above sentence, there aren't many friends but how much ever there are, have left.
Therefore, 'The few' is the answer.
For option D 'All' to be correct, there had to be 'the' in the question to form a correct grammatical sentence. (ALL the friends he had left him)