Why are "good morning", "good afternoon", and "good evening" introductions but "good night" is a kind of goodbye?

Read the following excerpt from "the city without us" by alan weisman: almost every other compound in nature contracts when frozen, but h20 (water) molecules do the opposite, organizing themselves into elegant hexagonal crystals that take up about 9 percent more space than they did when sloshing around in a liquid state. pretty six-sided crystals suggest snowflakes so gossamer it's hard to conceive of them pushing apart slabs of sidewalk. which statement best describes the effect of the metaphor on the excerpt's meaning? o a. it likens h2o molecules to hexagonal crystals, which are actually larger than people imagine. o b. it makes the frozen crystals seem like friends to the city to contrast with what a deceitful foe they are. o c. it compares the sloshing liquid to a river of water able to push apart the sidewalk o d. it compares the frozen crystals to delicately lacy snowflakes having an unexpected strength (apex)