可使粪便化学法隐血试验出现假阴性的物质是（）

A.铁剂

B.铋剂

C.维生素C

D.动物血

E.食物鱼肉

--- May I go and play with Dick this afternoon, Mum?

--- No, you can’t go out _____ your work is being done.

A．before

B．until

C．as

D．the moment