To improve their oral English, everyone in the class is supposed to ______ actively in these discussions.
A. participate B. attend C. enter D. take
Stronger and more lasting memories are likely to be formed ________a person is relaxed．
A．where B．unless C．when D．although
Nearly four hundred supermarkets in Beijing are preparing to dim(使暗淡) their lights ________ the "Earth Hour 2010" on Saturday night．
A．honor B．honoring C．to honor D．having honored
A salty diet may increase the risk of stomach cancer ________ 10 percent, South Korean researchers found in a study of more than 2 million people．
A．at B．to C．by D．for
The first textbooks ______ for teaching English as a foreign language came out in the 16th century.
A. to be written B. written C. being written D. having written
Some people are worrying about the possibility ________ mobile phones could be responsible for a range of illnesses, from rashes(皮疹) to brain tumors．
A．that B．why C．how D．whether
