I help prevent dryness, but when I am in excess I can lead to precipitation. who am i pls answer as fast as possible

The answer for #3 is c but i don't know why

An alcohol thermometer makes use of alcohol's changing in order to measure temperature. as the temperature goes up, the alcohol contained in the thermometer increases in volume, filling more of the thermometer's tube.

Can someone me with 3 and 4 plz. this is for masteries test.