单项选择题

The noise-killing system is not yet popular mainly because ______.

A．it is still being tried out
B．drivers still have their doubts
C．it increases the cost of car production
D．carmakers are not sure if it is necessary
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单项选择题
What does the second paragraph mainly discuss
A．Some animals and plants depend on each other for existence.
B．Some animals and plants develop their relationship easily.
C．Some plants depend on each other for food.
D．Some animals live better together.
单项选择题
When she took a mop from the small room what Mum really wanted to do was ______.
A．to clean the floor
B．to please the nurse
C．to see a patient
D．to surprise the story-teller
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