The computer system________suddenly while he was searching for information on the Internet.
A:broke up
B:broke away
C:broke out
D:broke down
实验室现有98%的浓硫酸,但实验中经常要用到较稀的硫酸。现要把50g质量分数98%的浓硫酸稀释成20%的稀硫酸,需加入多少克水?