Like other animals, we are          until we know it is safe to relax.

on purpose

on fire

on guard

on duty

考查介词短语辨析。句意：像其他动物一样，我们在知道安全的时候才放松警惕。A.on purpose 故意；B. on fire着火；C.on guard 警惕；D.on duty值班。结合后文we know it is safe to relax，可知我们在知道安全的时候才放松警惕。故选C项。

We played well, but I felt the team were            by one member, who didn’t try his best on the court.

let down

turned down

picked up

cheered up

考查动词短语辨析。句意：我们打得很好，但我觉得有一个队员在场上没有尽最大努力，让整个球队失望了。A. let down 使失望，放下；B. turned down 拒绝，调小；C. picked up捡起，接；D. cheered up使兴奋，振奋。结合句意可知，“有一个队员在场上没有尽最大努力”，所以“我们”感到失望。故选A项。

We cannot           the punctual arrival of trains in foggy weather.

get

help

guarantee

guess

考察动词词义辨析。句意：我们不能保证火车在雾天准时到达。A. get得到，获得；B. help 帮助；C. guarantee保证；D. guess猜测。根据句意可知，火车无法保证按时到达。故选C项。

There                   in the world              China is a great country with a long history and rich culture.

are no doubt; that 

are not doubts; if

is no doubt; that

is not doubt; if

考查固定句型和同位语从句。句意：毫无疑问，中国是世界上有着悠久历史，丰富文化的一个大国。分析句子可知，这个句型为 there is no doubt that 引导，表示“毫无疑问......”.本句为that that 引导的同位语从句，句意和句子结构完整。故选C项。

         Jixi today is more beautiful now. Mr.Jakson said he would visit it         third time.

The; /

The; the

/; a

The; a

考查冠词。句意：今天的鸡西市更漂亮了。Jakson先生说他将又一次来到这里。第一空“鸡西市”应用定冠词；第二空“不定冠词a/an+序数词+名词” 强调在已知数量上在累加一个，且 third为辅音音素开头的单词，应用a。故选D项。