When it ________ air pollution, Beijing faces the three “C”s, cars, coals and construction, which lead to Beijing’s thick air pollution.
| A．refers to | B．comes to |
| C．happens | D．speaks to |
Please excuse me _______ your letter by mistake.
| A．to open | B．to have opened |
| C．for opening | D．in opening |
After describing the planned improvements, she went on _______ how much they would cost.
| A．to explain | B．explaining |
| C．to be explaining | D．having explained |
The film star walked to his car, ______ a crowd of journalists.
| A．followed by | B．following by |
| C．to follow | D．to be followed by |
_______ on time, this medicine will be quite effective.
| A．Taking | B．Being taken |
| C．Taken | D．Having taken |
When I handed the report to John, he said that George was the person _______.
| A．to send | B．for sending it |
| C．to send it to | D．for sending it to |