新人求教几道GWD数学，谢谢！！！

Lucy小弱弱

For a nonnegative integer n, if the remainder is 1 when 2n is divided by 3, then which of the following must be true?
I 、n is greater than zero.
II 、3n = (-3)n
III、√2n  is an integer.
A.        I only
B.        II only
C.        I and II
D.        I and III
E.        II and III

If a committee of 3 people is to be selected from among 5 married couples so that the committee does not include two people who are married to each other, how many such committees are possible?
A\20  B\40  C\50  D\80  E\120

A driver completed the first 20 miles of a 40-mile trip at an average speed of 50 miles per hour.  At what average speed must the driver complete the remaining 20 miles to achieve an average speed of 60 miles per hour for the entire 40-mile trip?  (Assume that the driver did not make any stops during the 40-mile trip.)
A\65 mph  B\68 mph  C\70 mph  D\75 mph  E\80 mph  (答案是75，想不通啊，，，)

Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day.  If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper B, which of the following expresses r in terms of p?
100p / (125 – p)
150p / (250 – p)
300p / (375 – p)
400p / (500 – p)
500p / (625 – p)（这道题是不是没答案啊？）

A certain university will select 1 of 7 candidates eligible to fill a position in the mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in the computer science department.  If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?
A、42  B、70  C、140  D、165  E、315

Lucy小弱弱

大神求救啊~~~自己顶一个！