Which is the adjective phrase in the sentence?

Especially with suburban sprawl, trolleys are a better substitute for smelly buses.

A.

for smelly buses

B.

with suburban sprawl

C.

a better substitute

I think its A

Can you explain what you think and why?

It is the letter A and the adjective is smelly because that word qualifies the name, that are the buses. Can also be the letter C because the word "better" is doing see how is the quality of the substitute. which means that also qualifies the name