机车车辆2s走过2节10m的钢轨，则速度为（）km/h。
A.36
B.25
C.20
D.30
参考答案：A
Mr Johnson _______ a child at the start of the 1950s. [ ]
A. is
B. are
C. was
D. were
将下列维生素或无机盐与其相应的缺乏病用直线连接．
A、维生素A a、坏血病
B、维生素C b、地方性甲状腺肿
C、碘 c、佝偻病
D、钙 d、夜盲症
E、维生素B1 e、脚气病．
