`underline("A dark horse")`

Options

A. no longer in use
B. self-possessed
C. a competitor of unknown capabilities
D. an unfortunate person

Answer

C

Explanation

a dark horse: a person who has a surprising skill or ability: a competitor about whom little is known but who unexpectedly wins.
Anna.s such a dark horse - I have no idea she.d published a novel. The best option is a competitor of unknown capabilities