Triton's orbit was probably quite elliptical when it was first captured, but it is now quite circular. The mechanism for affecting this change is tides raised on the surface of by Triton.

Neptune

Explanation:

Triton's orbit was probably quite elliptical when it was first captured, but it is now quite circular. The mechanism for affecting this change is tides raised on the surface of Neptune by Triton. This caused Neptune moon Triton spiraling in towards the planet due to tides raised on the surface of Neptune.  

the answer would be c. motion and direction

i hope this : )