单项选择题

According to the passage, the cattle helped promote the growth of the wild grasses by

A．stepping on and pressing the seed into the ground
B．naturally fertilizing the soil
C．continually moving from one grazing area to another
D．eating only small quantities of grass

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单项选择题

Which of the following can be inferred about the cultivated grass mentioned in the second paragraph

A．Cattle raised in the eastern United States refused to eat it.
B．It would probably not grow in the western United States.
C．It had to be imported into the United States.
D．It was difficult for cattle to digest.

单项选择题

Which of the following was seen as a disadvantage of the postage stamp

A．It had to be purchased by the sender in advance.
B．It increased the cost of mail delivery.
C．It was difficult to affix to letters.
D．It was easy to counterfeit.