“We left the diner late because we saw some old friends” is the sentence with a clause used as a modifier to the verb.
Answer: Option 2
Explanation:
In the given sentence, the word ‘left’ denotes the verb action did by the subject ‘we’. And, we familiar about the modifier. It actually explains the action with where, when, why and how it probably happened.
From this clear explanation, we see that the phrase “because we saw some old friends” in the given sentence elaborated the action’ reason which verb denotes. So, concluding that Option 2 is correct sentence in using modifier with clause to the verb.