Question

In which sentence does the adverb clause modify an adjective?

I recognized as many flags as he.

The veteran appeared proud as he saluted the flag.

There are specific rules to know before you display the American flag.

Although the flag should always be raised quickly, it should be lowered slowly.

Answer 1

The sentence in which the adverb clause modifies an adjective is the second one - The veteran appeared proud as he saluted the flag.
The adjective here is proud, and the adverbial clause is as he saluted the flag. As you can see here, that clause is describing the adjective in more detail. 
When did the veteran appear proud? - As he saluted the flag (it obviously modifies the word proud)

Answer 2

Answer:

The veteran appeared proud as he saluted the flag.

Explanation:

The adverb clause is as he saluted the flag. It modifies the adjective proud.