The police were seeking more information to find out ______ the rich merchant.
| A．who was it that killed | B．who it was that killed |
| C．it was who killed | D．who was it killed |
Radium salts，which have been found to ______ in bones，give rise to bone cancer.
| A．pile up | B．build up | C．keep up | D．pull up |
Our teacher insisted that the key words worth paying attention _______ before class.
| A．be underlined | B．being underlined |
| C．to be underlined | D．to being underlined |
With some technical problems to be solved, it may be a while _______ the system is put into use.
| A．when | B．after | C．since | D．before |
That is the only way we can imagine _______ the overuse of water in students’ bathrooms.
| A．reducing | B．to reduce | C．reduced | D．reduce |
A great deal of advanced science and technology has been _______ since China carried out the reform and opening policy.
| A．brought down | B．brought in | C．brought out | D．brought up |