Which is correct?

Merge, Mainstream

Absorb

Which is correct?

Affect, Effect, Influence

Acid

Which is correct?

Acid

Nearing, Approaching

Which is correct?

Stimulate, Stimulation

Benefit

Which is correct?

Nearing, Approaching

Affect, Effect, Influence

Which is correct?

Cycle

Equator

Which is correct?

Necessary

Continue, Persist

Which is correct?

Release 

Cycle

Which is correct?

Fact

Benefit

Which is correct?

Absorb

Necessary

Which is correct?

Fact

Observe, Observation

Which is correct?

Evaporate

Release 

Which is correct?

Evaporate

Observe, Observation

Which is correct?

Merge, Mainstream

Equator

Which is correct?

Continue, Persist

Stimulate, Stimulation