单项选择题

All three circles shown have radius 1 and are tangent to each other. Find the perimeter of the shaded region.（）

A. 3
B. π
C.
D. 2π
E. 3π

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单项选择题

When 9 students took a zoology quiz with a possible score of 0 to 10 inclusive, their average (arithmetic mean) score was 7.5. If a tenth student takes the same quiz, what will be the least possible average score on the quiz for all 10 students （）

A.6.5
B.6.75
C.7.0
D.7.25
E.7.5

单项选择题

Josh works on the second floor of a building. There are 10 doors to the building and 8 staircases from the first to the second floor. Josh decided that each day he would enter by one door and leave by a different one, and go up one staircase and down another. How many days could Josh do this before he had to repeat a path he had previously taken（）

A.80
B.640
C.800
D.5040
E.6400

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