The farmer raises ten ____ .
A. sheeps
B. deers
C. cows
D. childs
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——Where’s Zhang Ying?——He’s gone to his teacher for _____about his homework.
A. advice
B. the advice
C. an advice
D. advices
There are many ____ in my little brother's box.
A. mouses
B. leafs
C. sands
D. toys
____do they have?
A. How much cattle
B. How many cattle
C. How many heads of cattle
D. How many cattles
在迈克尔逊干涉仪的一支光路中，放入一片折射率为n的透明薄膜后，测出两束光的光程差的改变量为一个波长，则薄膜的厚度是（）
A. λ/2
B. λ/(2n)
C. λ/n
D. λ/2(n-1)
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