"Millions of gallons" is not a verb; it is a noun phrase that refers to a large quantity of liquid measured in gallons. In this phrase, "millions" quantifies "gallons," indicating a vast amount. If you meant to ask about a specific verb related to this phrase, please clarify!
Millions and millions.
millions of gallons of water
360,000 gallons
millions of gallons
A linking verb.
A linking verb
It is an irregular verb.
The verb appear can be a linking verb or an action verb.
26 millions
An auxiliary verb
the infinative
It is a regular verb