An adjective used in a sentence has two functions i.e. Attributive and Predicative. Attributive use of an adjective is when it used before a noun for example He is a brave man.
An adjective has its predicative use when is used with a verb for example He is brave.
Capable is an adjective which is used as predicative and it is not used in Attributive case. For example He is capable. It is wrong to say He is a capable man. So answer is B He is the man capable to do this work.