The MOST Plausible Explanation for the Retrograde Rotation (Rotation in a Direction

The MOST plausible explanation for the retrograde rotation (rotation in a direction opposite that of most other planets) of Venus is the

A) frictional slowing down and eventual reversal of Venus's rotation by tidal forces at a time when the planet had deep oceans over its surface.
B) frictional drag of its very dense atmosphere on the rotating planet throughout its history.
C) combined gravitational effects of its neighboring planets, Mercury and Earth.
D) impact of a massive object on it early in its history.