解析　句意为：在晚上他们用经过特殊训练的狗来看守羊群。watch over看守，监视，符合句意。

10.When he looked up，he suddenly found himself by a group of teenagers，

looked at him anxiously.

A.to be surrounded；which

B.surrounded；who

C.be surrounded；who

D.having been surrounded；which

答案　B

解析　found oneself surrounded发现自己被包围着；who指代teenagers，引导非限制性定语从句。故选B。

Ⅱ.完形填空

　　The opening and closing of doors are the most significant actions of man's life.What a 11 lies in doors!

　　No man knows what awaits him when he opens a door. 12 the most familiar room，where the clock ticks and the hearth glows red at dusk may harbor 13 .The worker may actually have called and 14 the leaking pipe.The cook may have been ill and demanded her passports.

　　There are many kinds of doors.Revolving doors for hotels，shops and public buildings.They are 15 the busy，bustling ways of modern life.Can you 16 William Shakespeare or Charles Dickens skipping through a 17 door？There are double doors，sliding doors，stage doors and glass doors.The 18 and mystery of a door lies in its quality of being hidden.A glass door is not a door at all，but a window.The meaning of a door is to 19 what lies inside；to keep the heart in suspense.

　　Also，there are many ways of opening doors.There is the cheery 20 of elbow with which the waiter opens the kitchen door.There is the sympathetic and awful 21 of the dentist's maid who opens the door into the operating room and，without speaking， 22 that the doctor is ready for you.

　　The opening of doors has in it some flavor of the 23 ，some sense of moving into a new moment.Even in 24 ，the opening of a door may bring relief.But the closing of doors could be 25 .A door closed brings 26 to an end.And there are degrees of sadness in the closing of doors.A door slammed is a confession of weakness.A door 27 shut may often be the most tragic gesture in life.

The opening and closing of doors is a part of the serious fluency of life.Life will not stay