What ______ you ______ when you father came back?

A．did, do

B．are, doing

C．were, doing

D．do, do

测定粘度时，粘度计在恒温槽内固定时要注意（）

A.保持垂直

B.保持水平

C.紧靠恒温槽内壁

D.可任意放置