— I rang you at about nine, but there was no reply.
— Oh, that was probably _____I was seeing the doctor.
| A．why | B．when | C．what | D．That |
Just as a famous Chinese saying goes, a timely heavy snow is a ______ of good harvest next year.
| A．mark | B．track |
| C．sign | D．appearance |
Those black clouds are a sure _____ that it’s going to rain.
| A．thing | B．mark |
| C．sign | D．one |
She raised her finger to her lips as _____ for silence.
| A．an idea | B．a mark |
| C．a sign | D．a word |
Shortly after the accident, _____ police were sent to the spot to keep order.
| A．dozens of | B．dozens | C．dozen of | D．dozen |
We already have ______ pencils, but we need two ______ pens.
| A．dozen of, dozen | B．dozens of, dozens |
| C．dozens of, dozen | D．dozens of, dozen of |