That tests can actually give measurement of the language skills of the students_______ by many teachers.

A．questioned

B．are questioned

C．is questioned

D．questioning

已经确定的稳定而均一的物质，它的数值已由决定性方法确定，所含杂质也已经定量，该物质为（）

A.一级标准品

B.二级标准品

C.校准品

D.样品

E.质控品