I instructed the patient to return tomorrow.
Tomorrow modifies which adverb?
Tomorrow modifies "to return."
To determine which adverb "tomorrow" modifies, one should break down the sentence and identify the verb that "tomorrow" is related to. In this case, the verb is "instructed."
To find the adverb modified by "tomorrow," ask the question: When did the instruction take place? The answer would be "tomorrow."
Therefore, "tomorrow" modifies the adverb "instructed." It specifies the time or moment at which the action of instructing the patient takes place.