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
—Have you heard about Apple iPhone 4?
—Sure．It is very hot these days．I'm thinking about getting _______．
A. one B. them C. that D. it
