He was discharged on the fourth hospital day. verb = discharged, he= subject

questions hopefully fixed and are correct now...
After 24 hours in the hospital he was much improved. improved is a predicate adjective but now is the verb = was and the subject = he

Repeated chest x-rays, however, have shown atelectasis. repeated = verb, chest x-rays = subject = have

The complete verb is

was discharged.

The second is correct.

In the third sentence, "repeated" is used as an adjective modifying "x-rays." The subject is x-rays. The verb is have shown.