I Want to Know Why My Yard Is So Well

Multiple Choice

I want to know why my yard is so well lit at night.So I watch it over a period of several nights and notice that it is most well lit when the moon is full, less well lit at quarter moon, and most poorly lit at new moon.Therefore, I conclude that moonlight is principally responsible for lighting my yard at night.Which method did I use to determine this?

A) agreement
B) difference
C) joint method
D) concomitant variations
E) residues