1) He dived INTO the water.
2) He sent me a picture of HIMSELF.
3) I want you to be painted by ME.
4) One thing that really surprised me WAS so many cyclists.
=>Note, "one thing" is the subject and it's singular, so the verb should also be singular, "was".
5a) He said the city IS (it's a fact) . . .
5b) He said the city WAS (at the time of his visit) . . .
Student or Learner