Her daughter was born ______ December 10, 1998.
[ ]
A. at
B. in
C. on
D. during
答案:C
某同学利用家中废旧材料制作一个可使玩具扬声器发出声音的电池,装置如图所示。下列说法不正确的是
A.电流方向为:铝质易拉罐→导线→扬声器→导线→炭棒
B.铝质易拉罐将逐渐被腐蚀
C.电池总反应为:4Al+3O2+6H2O=4Al(OH)3
D.炭棒上发生的主要反应为:O2+4e-+2H2O=4OH-
氟化水源防龋的标准浓度是
A.0.05~0.1ppm
B.0.1~0.5ppm
C.0.5~1ppm
D.1~5ppm
E.5~10ppm