30．Students should ____to smoke ．

A．not be allowed        B．be not allowed      C．not allowed           D．be allowed

29．The students shouldn’t _____on school nights because having a good sleep can help them with study．

     A．deal with                                          B．obey school rules

C．stay up                                             D．study in groups

28．Nothing else can stop the sandstorm _____more and more trees are planted．

   A．unless                  B．if                       C．when                    D．while

27．―Look! How dirty the river is!

   ―It ______clean before the factory was built nearby．

A．used to be              B．will be                  C．has been               D．is

26．The teacher has taught in the small school ______．

A．since thirty years                                      B．thirty yeas ago

C．for thirty years ago                                  D．since thirty years ago

25．―Would you like some coffee or tea?

―______．I’d like some orange．

A．Either                  B．Both                   C．Neither                D．Each

24．She used to be outgoing ,___?

   A．doesn’t she?         B．does she?             C．didn’t she?          D．did she?

23．It’s not easy to live in a foreign country ,_____if you don’t understand its language．

   A．really                    B．especially           C．exactly                D．usually

22．―I haven’t been to a science museum．

 ―_____________．

   A．Me too．               B．So am I．         C．So have I              D．Me neither．

21．You ____Beijing twice．What do you think of it ? 

   A．were going to        B．have been to         C．are going to                 D．have gone to