Answer:
When someone decided to check on me for the first time in years. Man, it's so relieving to know someone has your back and someone cares.
Momentum depend on Mass and velocity
A is the most suitable answer, although all of the answers are technically correct. B, C and D all serve to add <em>clarity</em> to an essay, which in turn adds interest. A directly adds interest, and the clarity comes as a secondary effect.