Question

what does it mean for a membrane to be selectively permeable?
only certain molecules are allowed to pass through.
the membrane is rigid and only allows water to pass through.
all types of molecules are able to pass into the cell.
the membrane is rigid and nothing can enter or leave the cell.

Explanation:

A selectively permeable membrane controls what enters and exits the cell. It is not rigid (eliminating options with "rigid"). It doesn't allow all molecules (eliminates "All types...") and isn't impermeable (eliminates "nothing can..."). "Only certain molecules..." aligns with the definition of selective permeability.

Answer:

Only certain molecules are allowed to pass through.