Often, an Asteroid Viewed from Earth Appears to Change Its

Often, an asteroid viewed from Earth appears to change its brightness periodically because the

A) albedo is significantly different on one side than the other.
B) leading side is very dark and the trailing side is very bright like Iapetus, a satellite of Saturn.
C) asteroid is elongated, so it may present a larger or a smaller cross section to Earth as it rotates.
D) asteroid is simply passing through the shadow of another asteroid.