I'd go with this one: b.) Meiosis I separates tetrads, and meiosis II separates sister chromatids. As it is correctly describes the difference between meiosis I and meiosis II.
The word sponge is more appropriate to use than Underground river since an underground river can loose water while an aquifer cannot loose water, unless it is open-air and above ground. then the aquifer would slowly loose water due to evaporation from the sun.
