The Lunar Maria Appear Smooth Because They Are

The lunar maria appear smooth because they are

A) regions where craters have been obliterated by crustal deformation caused by hot spots and volcanic lava flow from the underlying molten mantle.
B) recent lava flows, occurring within the last billion years, that have obliterated earlier craters.
C) ancient lava flows that occurred soon after the end of an early period of intense bombardment and that have had relatively few impacts since then.
D) ancient sea beds, now dry, dating back to when the Moon had a denser atmosphere and rainfall was abundant.