For Water Fleas of the Genus Daphnia, Switching from a Pattern

For water fleas of the genus Daphnia, switching from a pattern of asexual reproduction to sexual reproduction coincides with

A) environmental conditions becoming more favorable for offspring.
B) greater abundance of food resources for offspring.
C) periods of temperature or food stresses on adults.
D) completion of puberty.
E) exhaustion of an individual's supply of eggs.