Identify the sentence that has an understood you as its subject.
a. has mr. burghardt returned yet?
b. while waiting, we reviewed our plans.
c. have another glass of orange juice.
d. looks can be deceiving.

"you" is an understood subject most often in IMPERATIVE sentences. these are commands, like, "go to your room" or "have a seat."

in those sentences, the subject is "(you) go to your room" or "(you) have a seat."

in the answer choices: mr. burghart is the subject in choice A. "we" is the subject in choice B. "looks" is the subject in choice D.

C has the understood you: (you) please have another glass of orange juice. because it's a command, it's assumed that you're addressing a certain person (you).