单项选择题

What is the average of four consecutive odd numbers starting with 2n+1（）

A. 4
B. 2n+3
C. 2n+4
D. 2n+5
E. n+4

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单项选择题

In the world of art, distinguishing the authentic piece from the forgery is not an easy feat and often requires the use of multiple experts. Millions of dollars can be at stake, yet even experts can be fooled. However, a recent discovery has introduced a new resource for galleries and other groups seeking to establish the origins of their paintings: mathematicians. Math experts were able to analyze digital images of authenticated paintings where they found consistent differences in paint texture. This consistency suggests that each artist has a unique style of brush stroke that cannot be completely duplicated.In the first two sentences of the passage, the author suggests which of the following（）

A. It is nearly impossible to determine whether a painting is authentic or fake without the use of math.
B. Even if multiple experts from various fields analyze a painting, it is not always possible to determine its authenticity.
C. New discoveries in art always lead to a greater degree of truth.
D. Art can be difficult to analyze, but mathematical models can help to find the truth.
E. Mathematicians have a great degree of expertise in analyzing art.

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