Final answer:
Fleas are stimulated to come out of diapause by environmental cues such as warmer weather conditions, increased day length, and vibrations indicating the presence of a host. Therefore, the correct option is A, B, D.
Step-by-step explanation:
Factors that stimulate fleas to come out of diapause include environmental cues such as changes in weather conditions and photoperiod. The summer season brings about warmth that facilitates the shift of energy resources in fleas towards reproduction. Another critical factor for breaking diapause is the increase in day length, which triggers hormonal changes necessary for fleas to exit diapause and become active again. Vibrations, which indicate the presence of a potential host, can also prompt fleas to emerge from diapause.