Sycamore street is not the longest street in our town, but it is longer than oak street.
which is the comparative adjective?

A comparative adjective is the conjunction of some sorts that gives up a signal that there is a comparison about to or that has taken place. In this example, the word "but" would be the comparative adjective because this is the signal word that a comparison has/is going to take place.
 Hope this helped!

That he won't be able to get a good job without a nose