一片玉米农田就是一个生态系统。在生产过程中，农民需不断对农田进行除草、治虫等活动，从

I got a job teaching special education at a school in Coachella, California, a desert town about 170 miles from home. It was no (1) job. Street gangs (2) around the school after dark.

"Be careful, " Dad warned me during one of my frequent weekend (3) home. He was concerned about my living (4) , but I needed to be on my own.

One evening, I stayed after school to rearrange my classroom. (5) , I turned out the light and closed the door. Then I (6) toward the gate. It was (7) ! I looked around. Everyone had gone home.

After (8) all the exits, I found just enough (9) to squeeze under a gate in the back of the school. Then I walked toward my car, parked in a field behind the building.Suddenly I heard voices. I (10) around and saw at least eight boys following me. (11) my pace, I reached into my shoulder bag to get my key. I (12) all over the inside of my handbag. But the key wasn’t (13) ! Dear Lord, please help me, I prayed (14) . Suddenly, my fingers touched a loose key in my purse. I didn’t even know if it was for my car, but I took it out and (15) it. It worked!I opened the door, slid in and locked it—just (16) the teenagers surrounded the car. Trembling , I started the engine and (17) away. When I returned to my apartment, the phone was ringing. It was my Dad. I didn’t tell him about my experience; I didn’t want to (18) him. "Oh, I forgot to tell you!" He said, "I had a (n) (19) car key made and slipped it into your purse—just (20) you ever need it. \

13().

A.there 

B.lost 

C.used 

D.inside

固定高压水枪的保护高度一般为()。

（A）10～20m 

（B）20～30m 

（C）30～40m 

（D）40～50m

成长小组组员之间已相当熟悉，聚会时均能积极表达自己的意见，讨论非常热烈，互不相让，还出现个别组员为获得更多的支持，出言贬低他人的行为。社会工作者小李细心倾听组员的意见，不时点头，并指出小组面临的冲突，让他们一起面对，寻求处理的办法。小李运用的小组技巧有（）。

A.情绪转移法

B.角色扮演技巧

C.积极给予回应

D.表达鼓励支持

E.促进互动交流

放射性气溶胶吸入显像常用的示踪剂为（）

A.^99mTc-HSA或^99mTc-DTPA气溶胶

B.^133mXe

C.^81mKr

D.^99mTc-MAA

E.¹³³Xe-生理盐水

直流电压的采集采用电容式分压器原理，直接送入直流测量盘。