During endocytosis and exocytosis, cells

a) take in what they need and expel what they don't need
b) move water in and out through the cell membrane
c) actively transport molecules across the cell membrane

Take in what they need and expel what they don't need. (Ans. A)

Explanation:

Endocytosis and exocytosis are two active transport processes which are helping macro molecules present in the cytoplasm to move inside or outside the cell across the plasma membrane. It is an energy requiring movement.

Endocytosis is known as a process which is capturing the particles from outside the cell by engulfing of them with the cell membrane. Endocytosis is mainly two types:

1) Phagocytosis, in this process cell is engulfing whole particle. It is also known as cell eating.

2) Pinocytosis, in this process cell is engulfing already dissolved food. It is also known as cell drinking.

Exocytosis, in this process where vesicles fusing with the plasma membrane which helping them to move substances out of the cell.

i believe the answer would be b. hope it : )