What causes water molecules to stick together in liquid water? O A. Hydrogen bonds
B. Water vapor
C. Carbon dioxide
D. Sun's gravity

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Which layer will become saturated first when rain falls?

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.