She's upstairs _____ letters. [ ]
A. write
B. is writing
C. write
D. writing
答案:D
华兴会
依地酸钙钠对下列哪种重金属中毒效果较好
A.汞中毒
B.砷中毒
C.铜中毒
D.铅中毒
E.镍中毒