Is - two billion dollars is a unit, one unit so it is singular and you use the singular verb
think - scientists is a plural, therefore, you must use the plural verb form of think
A character’s interactions and feelings shape their personality, goals, etc. Knowing when and how they interact is essential.
1.the heads on Easter island and how they move
2. how the pyramids were built
3. how the temperature of the earth is changing
Dripped
A verb is a word that expresses an action: (she jumped into the pool - jumped being the verb) or a state of being: (an example being I am happy. Am is the verb here)
The ice cream was doing an action - it was dripping, so dripped is the verb
