平行移动拍照法
参考答案：
与被拍物体呈现平行状态连续拍照。
We _______ on it for several hours but we have not yet reached any conclusion.
A．work
B．areworking
C．havebeenworking
D．havebeenworked
连接装置的作用是什么？对其有哪些要求？
