C.The farmers couldn't leave without footprints.

　　D.The farmers couldn't keep the wheat straight up.

　　解析：事实细节题。根据第三段的内容可知，人们试图人为地制造一些类似的“怪圈”，可是他们的尝试以失败而告终，因为只要他们进入麦田，就必然会留下踪迹。

　　答案：C

　　4.One explanation given by scientists for the crop circles is that they are made by .

　　A.airplane crashes

　　B.air movement

　　C.unknown flying objects

　　D.new farming techniques

　　解析：事实细节题。由文章最后一段的内容可知B项符合题意。

　　答案：B

　　B

　　How to Be a Winner

　　Sir Steven Redgrave

　　Winner of 5 Olympic Gold Medals

　　“In 1997 I was found to have developed diabetes (糖尿病).Believing my career (职业生涯) was over，I felt extremely low.Then one of the specialists said there was no reason why I should stop training and competing.That was it —the encouragement I needed.I could still be a winner if I believed in myself.I am not saying that it isn't difficult sometimes.But I wanted to prove to myself that I wasn't finished yet.Nothing is to stand in my way.”

　　Karen Pickering

　　Swimming World Champion

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