According to Recent Research with College Populations,what Was Found to Be

According to recent research with college populations,what was found to be related to sperm production? 

A)  Sperm production was highest for college males who had several sexual partners. 
B)  Sperm production was lower during exam periods than at the beginning of the semester. 
C)  Sperm production was higher in students attending college in warmer parts of the U.S. (i.e., Florida, Texas) than those attending college in places with cooler climates (i.e., Minnesota, New York) . 
D)  Sperm production was highest for college males who masturbated daily.