单项选择题

Three red marbles and 2 white marbles are placed in an empty box．One marble at a time is to be selected randomly and removed from the box until all 5 marbles have been removed． What is the probability that each of the first 3 marbles removed will be red（）

A.A
B.B
C.C
D.D
E.E

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单项选择题
If those employees who made 6 or more errors were removed from the sample and an employee were selected at random from those remaining，what is the probability that the employee selected made no errors（）

A.A
B.B
C.C
D.D
E.E
单项选择题
If the average(arithmetic mean)of x，y，x，5 and 7 is 8，which of the following must be true（） Ⅰ．The median of the five numbers cannot be 5． Ⅱ．At least one of x，y，and z is greater than 9． Ⅲ．The range of the five numbers is 2 or more

A. Ⅰ only
B. Ⅱ only
C. Ⅲ only
D. Ⅰ and Ⅲ
E. Ⅱ and Ⅲ
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