Question

How to know the difference between adverb and adjective clause and how to know what they modify

Answer 1

EXAMPLE :

The pen, which you gave me, was lost.

Here the group of words, which you gave me - qualifies the noun the pen and does the work of adjective. It's adjective clause.

EXAMPLE :

I don't know why he was late.

Here the group of words, why he was late is a clause, as it has a subject - he, and a predicate - late, of its own. It's adverb clause