This old building is said _____ two years ago and a new high building now stands where the old one used to lie.

A．to have puller down

B．be pulled down

C．pull down

D．to have been pulled down

人在空旷的山谷中唱歌能听到回声，若从发出声音到听见回声用了0.8s，则反射声音的山峰离唱歌的人有多远？