My pain _____ obvious the moment I entered the office，for the first man I met asked pitifully，“Are you feeling all right？”

1. A.
   could be
2. B.
   could have been
3. C.
   must be
4. D.
   must have been

My pain _____ obvious the moment I entered the office，for the first man I met asked pitifully，“Are you feeling all right？”

A．could be                B．could have been      C．must be                  D．must have been