We can gain valuable experience from the mistakes which _____ to prevent them from happening again.

A．should be avoided                                      B．might be avoided

C．must have been avoided                              D．could have been avoided

下列句子中，每句都有一处错误。

增加：在缺词处加一个漏字符号(Λ)，并在其下面写出该加的词。

删除：把多余的词用斜线(﹨)划掉

修改：在错的词下划一横线，并在该词下面写出修改后的词。

1．For several billion year after the “Big Bang”, the earth was still just a cloud of dust.

2．How it was to become was uncertain until between 4.5 and 3.8 billion years ago.

3．The earth became so violently that it was not clear whether the shape would last or not.

4．As a result of this, many scientists believe the earth may become too hot to live.

5．So whether life will continue on the earth for millions of years to come will depend on whether this problem can solve.

6．They are putting too much carbon dioxide into the atmosphere, which prevent heat from escaping from the earth.

7．Thus they have, in our turn, become the most important animals on the planet.

8．This produced a chain reaction, which made it possible for life develop.

9．That many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas.

10．What is even more important is as the earth cooled down, water began to appear on its surface.

这些疑点只能以行动来消除。

Doubts could be ________ ________ only by deeds.

Smoking might be ________ ( 禁止，取缔 ) totally in most building in big cities. （根据汉语提示单词拼写）

It’s strongly recommended that the machine ________ every year.

A ． repair B ． to repair C ． be repaired D ． should repair