Besides its main use the noise killing system can

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

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