移项得,x2=4
开方得,x=±2,
故选D.
—Does your father ________ in a school?
—No, he doesn't. He ________ in a hospital. [ ]
A. work; work
B. works; works
C. work; works
D. works; work
需要50%的NaCl溶液1000ml,现有80%和25%浓度的NaCl溶液,将如何配置
A.需要80%145.5ml,25%854.5ml
B.需要80%344.5ml,25%656.5ml
C.需要80%336.5ml,25%633.5ml
D.需要80%454.5ml,25%545.5ml
E.需要80%498.0ml,25%502.0ml