The correct answer is 'If molecules are small enough, then they can pass through the semipermeable membrane because they can cross the semipermeable membrane from their small pores or openings'.
The semipermeable membrane is permeable to few molecules, and the smaller molecules pass through the molecules from small pores present in the semipermeable membrane. The size of the big molecules are large, so, they cannot cross through semipermeable membrane.
