Final answer:
Gases are capable of diffusing through a semipermeable membrane due to their smaller molecules.
Step-by-step explanation:
The correct answer is a. Gases. Gases are capable of diffusing through a semipermeable membrane. This is because gases have smaller molecules that can easily pass through the pores or small openings in the membrane. Solids and liquids, on the other hand, have larger molecules or particles that cannot easily pass through the membrane.