滴定磺酸中和值所用的试剂是（）标准溶液。
A.KHCO3
B.NaHCO3焦磺酸
C.H2SO4
D.NaOH
参考答案：D
小圆直径是5cm，大圆直径是10cm，大圆面积与小圆面积的比是______．
—How do you usually come to school?
—____ my father's car. [ ]
A. By
B. With
C. In
D. For
