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【单选题】
一牧场上的青草每天都匀速生长。这片青草可供27头牛吃6周，或供23头牛吃9周。那么可供21头牛吃几周？（）
A.
8
B.
10
C.
12
D.
14
参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Increasingly, over the past ten years, people--especially young people--have become aware of the need to change their eating habits, because much of the food they eat, particularly processed food, is ...
A.
they are fed on food which is little better than garbage
B.
they live in very crowded condition
C.
the eggs they lay lack vitamins
D.
they are allowed to move about and eat freely
【单选题】Increasingly, over the past ten years, people--especially young people--have become aware of the need to change their eating habits, because much of the food they eat, particularly processed food, is ...
A.
they are more health conscious
B.
they want to taste all kinds of foods
C.
natural foods are more delicious than processed foods
D.
they want to return to nature
【单选题】在“青草→食草昆虫→蜘蛛→食虫鸟→猫头鹰”这条食物链中，占生态系统总能量比例最多和最少的消费者依次是（ ）
A.
猫头鹰和食草昆虫
B.
青草和猫头鹰
C.
食草昆虫和青草
D.
食草昆虫和猫头鹰
【单选题】As our van pulled up to the ranch (牧场) to start a three-month program for troubled boys, we passed a cowboy on his horse. Bill was the owner of the ranch. We made eye contact through the dusty window ...
A.
seriousness
B.
friendliness
C.
authority
D.
generosity