Answer:
D. Gravity
Step-by-step explanation:
Gravity cannot be a source of centripetal force. Gravity is the force of attraction from between all masses in the universe; especially the attraction of the earth’s mass for bodies near its surface; “gravitation cannot be held responsible for people falling in love” with Albert Einstein.
It manner that is serious and solemn. A solemn and dignified feeling.
Therefore, the correct answer is d. gravity.