C．kill D．reduce

　　解析：选A　从词语搭配考虑，本句告诉读者，种庄稼之前需要平整土地和除草，remove weeds意为"清除杂草"。

　　15．A.destroy B．prevent

　　C．divide D．limit

　　解析：选A　让牛羊在地里走是为了摧毁杂草或者吃掉杂草，故选destroy。

　　16．A.keep B．improve

　　C．manage D．change

　　解析：选D　从下句中"do not plant rice __17__ in the same field"可知庄稼要换着种，因此选change。

　　17．A.one after another B．here and there

　　C．now and then D．year after year

　　解析：选D　year after year"年复一年"，意为"不在同一块地里年复一年地种同一种庄稼"。

　　18．A.win B．collect

　　C．harvest D．plant

　　解析：选C　本句意在表达"如果每年换种不同的庄稼就会有好收成"。harvest good crops意为"收成好"。

　　19．A.holes B．lines

　　C．space D．balance

　　解析：选C　从词语搭配考虑，本句指的是"种植小麦时，株与株之间要留有空间"，而非留有线、洞或平衡，因此选space。

　　20．A.showed B．meant

　　C．intended D．decided

　　解析：选A　前面有Jia did experiments，因此后面是实验结果"证明，表明"，因此选showed。

　　Ⅱ.短文改错

　　I was often laughed at my classmates before I turned 14 because I was always very nervous when talking to someone. Helpful and sad, I felt that I could do nothing. You can not imagine what great difficulty I have in my life. And later, something happened, what changed my life completely. It was an English speech contest and my mother encouraged me to take a part in it. I tried my best to remember the whole speech "Believe in yourself" and practiced them over 100 time. Believing it or not, I finally won first prize. Hearing the cheers from the teachers and students, I stood here, with my eyes full of excited tears.

答案：第一句：my前加by