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
The biggest advantage of this product is that ______.
A．it will be faster and cheaper than manual labor
B．it can climb mountainsides, drill holes, insert bars and cement
C．it can collect data on the slope' s stability
D．it can drill without a human being on board
单项选择题
What does the robot look like
A．A human being.
B．A spider.
C．A truck.
D．A drill.
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