-Why does the Lake smell terrible?
-Because large quantities of water .
| A．have polluted | B．is being polluted | C．has been polluted | D．have been polluted |
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 |
Jim is ______ person, and everyone is willing to be ______ with him.
| A．so kind a, friends | B．so a kind, friends |
| C．so kind a, friend | D．so a kind, friend |