A study ________ in the USA in 1977 showed that the chemical ASA in aspirin could prevent a stroke.
| A．carrying out | B． carried out | C．working out | D．worked out |
Studies show that people are more to suffer from back problems if they always sit before computer screens for long hours.
| A．possible | B．likely | C．probable | D．sure |
Ricky stepped forward to front of the stage and began to sing in loud voice.
| A．the, a | B．the, the | C．/, a | D．/, the |
but he still can not understand it.
| A．Told many times |
| B．Having been told many times |
| C．He has been told many times |
| D．Though he has been told many times |
Mr. Lee, who as a guide for over 10 years, is now a manager in a big travel agency.
| A．worked | B．has worked | C．had worked | D．works |
In the school hall, where a meeting , some students are busy preparing for it.
| A．is held | B．has been held | C．is being held | D．is to be held |