When Mariner 10 Passed by Mercury, the Caloris Basin Was

When Mariner 10 passed by Mercury, the Caloris Basin was crossed by the terminator line. Which statement correctly evaluates this situation?

A) This is not surprising because the Caloris Basin is so large that the terminator line always crosses part of it.
B) This is not surprising. Because of Mercury's synchronous rotation orbit, the terminator line does not move across the face of the planet, and it lies perpetually on the Caloris Basin.
C) Because of Mercury's 3-to-2 spin-orbit coupling the terminator line moves slowly across the face of Mercury. When Mariner 10 flew by it happened to lie across the Caloris Basin.
D) There is a direct correlation between the Caloris Basin and Mercury's unusual rotation. This unusual rotation occurs because of the bulge on Mercury-and this was caused by the impact that produced the Caloris Basin. So, it is not surprising that the terminator line was found across the Caloris Basin.