Step 1: Recall the effect of crosswind.
A crosswind acts perpendicular to the aircraft's intended direction of travel.
It tends to push the aircraft sideways, producing drift.
Step 2: Determine its primary effect.
To maintain the desired runway alignment or flight path, the pilot must apply appropriate control inputs.
Thus, a crosswind mainly affects
\[
\boxed{\text{Directional control}.}
\]
It does not directly alter lift or engine power.
Therefore,
\[
\boxed{\text{Directional control}}
\]
is the correct answer.
Thus,
\[
\boxed{(C)}
\]
is the correct answer.