Given that a blowfly starts its lifecycle only if there are appropriate conditions met, one of which is suitable temperature, the correct answers as to what can impact the timing of the blowfly lifecycle is the air temperature.
I don't see how humans will impact when this fly is going to be born, so A and C are incorrect. Leaves also doesn't really affect blowflies, which is why D is incorrect as well.
Use pesticides, kill the cockroaches
use cockroaches for research XD
and other than that, live in harmony with them i guess?
nothing else you could really do about it
Needed:
Co2
Water
Solar Energy(Sunlight)
Produced:
02
Glucose for the plant to use for survival
A i think could be wrong but i dont think so