25℃时,向100克质量分数为5%的氯化钠溶液中加入5克氯化钾粉末,完全溶解后,溶液中氯化钠的质量分数将( )
A.减少
B.增加
C.不变
D.无法判断
答案:A
— I visited the Purple Mountain Observatory last Sunday.
—______ Why didn’t you tell me earlier?
A.You did?
B.I hope so.
C.Have a good time!
D.It’s so kind of you.
红外检测中绝对黑体的发射率为()。
A.0
B.0.1
C.0.9
D.1