In the above sentence, the word 'incapable' means 'not able to'.
C) not able to
Explanation:
The sentence talks about the inability of the person. The phrase 'not able to' is equivalent to the word 'incapable'. The meaning of 'incapable' is unable t achieve something. According to the above sentence, the person was unable to sing and hence, he is said to be incapable of the ability to sing.
