用于侧向通过列车,速度不超过50km/h的单开道岔,不得小于()号。
A.9
B.12
C.18
D.30
参考答案:B
杭州市教育局开展支教活动,有五位高级教师被随机分配到A,B,C三个所不同的学校,且每所学校至少分配一名教师.
(1)求甲、乙两位教师同时分配到一个中学的概率;
(2)设随机变量X为这五位教师分到A中学的人数,求X的分布列和期望.
— Do you know what time the accident happened yesterday?
— I'm not sure. Maybe at 2:30 pm. I _____ at the department store at that time.[ ]
A. shop
B. was shopping
C. am shopping
D. shopped