Why is it sometimes difficult for ecologists to design controlled experiments?

Mike has a problem with his testosterone. he is unable to produce enough. which will most likely be affected by his inability to produce testosterone? check all that apply.

Cedric has a low fever and minor aches. yesterday, he went to the doctor for his booster shot and receive the flu shot. which best explains why he has this reaction?

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic