When a machine of this kind is ________, the materials must be carefully chosen for its parts.
When a machine of this kind is ________, the materials must be carefully chosen for its parts.
A.built
B.building
C.to build
D.to be built
答案及解析: D
When a machine of this kind is ________, the materials must be carefully chosen for its parts.
A.built
B.building
C.to build
D.to be built
答案及解析: D