有关明胶的说明，错误的是（）

A.是一种蛋白质

B.属于乳剂层成分

C.起介质和保护作用

D.来源于动物体

E.自身有感光作用

What is the process for aggregating the estimated costs of individual activities or work packages to establish a cost baseline known as ？（）

A．Cost assessmen

B．Determine budge

C．Plan contractin

D．Cost estimatin