What forms the structure called a coral reef

Read these sentences from the text. near the equator, the tropics receive the most rain on a consistent basis. as a result, the fresh water falling into the ocean decrease the salinity of the surface water in that region. [. .] . . as the salt content of sea water increases, so does its density. what can you infer about how rain affects the density of surface water near the equator?

May someone me with these science questions

Which of the following volumes is the smallest? a) one microliter b)one deciliter d)one liter c)one milliliter