She was so________in her job that she didn’t hear someone knocking at the door.

A．absorbed

B．attracted

C．drawn

D．concentrated

家庭中常用的拉窗帘的装置中就运用了滑轮．请你仔细观察一下，这种装置是怎样设计的，为什么只要拉动窗帘绳就能使窗帘左右移动？