SAT2物理OG上的两道题……求帮忙解答……

1 If two electrically charged particles repel each other with forces of equal magnitude, then the charges must

(A) have different magnitudes

(B) have the same magnitudes

(C) have different signs

(D) have the same sign

(E) be seperated by unit distance

2 Two identical, human-looking robots are standing and facing forward in seperate spaceships. Both ships are moving at 0.8c but are travelling in opposite directions, as shown above. If a person on the spaceship with robot A could make measurements on both robots, which of the following would the person observe to be different?

(A) the robot's heights

(B) the length of the robot's feet from toe to heel

(C) the width of the robot's faces

(D) the length of the robots' legs

(E) the width of the robots' shoulders

第一题的答案是D 第二题答案是B 谁能告诉我为什么...