Select the most appropriate word to fill in the blank. Robert and Rooney aren't very good friends although they _______ each other for a long time. (a) have known (b) are knowing (c) has known (d) knew

Options

A. have known
B. are knowing
C. has known
D. knew

Explanation

“have known” should be used.
RULE: The Present Perfect is used to say that an action happened at an unspecified time before now.
“Have” is used for plural.