Answer:
Its D, The cell membrane(also known a the plasma membrane) has a job in which it has to allow passage in and out of the cell. Therefore it can prevent harmful substances from entering the cell. Think of it as security, either allowing you access or denying you depending on if you're a threat
I believe studying the hydrosphere would be most important because we haven't explored a good majority of it yet so we need to explore our waters before we explore space
Brown. Your pigmentation in pregnancy is browner
the step in step 2 is wrong
