Question

What does the bolded phrase describe?

Carriages used to be drawn by horses.
What does by horses describe?

Answer 1

The verb drawn.

Step-by-step explanation:

By horses is an adverbial phrase describing the verb 'drawn'.

Answer 2

The word "drawn"

Step-by-step explanation:

The phrase "by horses" describes the verb "drawn" since it is a verbial phrase.