—Susan, why are you still here? They are all ready to start.        

—I'm sorry, but I ________when to start.          [ ]

A. was told    

B. told            

C. tell              

D. wasn't told

下列化学方程式符合题意，且书写正确的是（　　）

A．用盐酸除去铁锈   Fe₂O₃+4HCl═2FeCl₂+3H₂O

B．验证铜的活动性比银强  Cu+2AgCl═CuCl₂+2Ag

C．检验二氧化碳气体   CO₂+Ca（OH）₂═CaCO₃↓+H₂O

D．制取少量硫酸镁    MgCl₂+Na₂SO₄═MgSO₄+2NaCl