Animal migration on savannas is often governed by distance
reproduction
rainfall
fire

The answer would be rainfall.

Explanation:

The reason why this is the answer is because rain is essential for survival in such a hot and dry climate. Droughts are quite frequent in the savanna and the lack of water leads to the death of many organisms.

b would be the right answer

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.