My book says:" Adverbs that have the same form as adjectives have comparatives with -er."?

Question

Example: 1. Ted drives faster than Bill.
2.Bill drives slower/more slowly than Ted.
The adjective n adverb of "slow" are not the same.so why both slower or more slowly?

Answer 1

slow is an adjective, slowly is an adverb.

Is that what your book says? It just seems like it doesn't explain the functions of adverbs very well.

An adjective modifies (describes) nouns and pronouns.
Adverbs modify verb, adjectives, and other adverbs.