One who able to use the right and left hands equally well:

The correct answer is B. Ambidextrous.

A person who is ambidextrous is able to use both their right

Sinister is an adjective that means “evil” or “unlucky.” It is not related to the ability to use both hands.

Ambivalent is an adjective that means “having mixed feelings about something.” It is not related to the ability to use both hands.

Amateur is a noun that means “a person who does something for pleasure rather than as a job.” It is not related to the ability to use both hands.