I can’t buy this bike, because it is_____ expensive.

31. The decision ______ Internet addictionas a mental disorder hascaused much debate.

I often hear him ______.Today when I pass(经过)the classroom, I hear him ______again .

Since the Obama administration took office,the China—US relations ________ positive development thanks to joint efforts ofboth sides, President Hu said at the Nuclear Security Summit inWashington, April,12,2010.

Co-operation or teamwork, the importance of which is often ________, plays an important part in football matches.