Mercury's Average Density Is About 50% Greater Than the Moon's

Mercury's average density is about 50% greater than the Moon's, even though the two bodies have similar radii. This suggests that Mercury('s)

A) interior is much richer in iron than the Moon's.
B) contains proportionately far more rock than the Moon.
C) greater mass has prevented its gravitational attraction from compressing it as much as the Moon's is.
D) must have a liquid water core.