—Have you seen _____ empty box?

—Do you mean _____ box you showed to me yesterday? I put it in your

schoolbag.[ ]

A. a, the    

B. an, a    

C. an, the

D. the, a

托盘的种类按结构可以分为（）。

A.平板托盘

B.箱型托盘

C.立柱型托盘

D.折叠式托盘

E.两面托盘