You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: For positive integers x and z, which of the following can be written as z^2?

 Option A: x^2+1

 Option B: x^2-1

 Option C: x^2-24

 Option D: x^2+11

 Option E: x^2-11
[A]: Option D


[Q]: Question: If x < y < 0, which of the following must be true?

 Option A: 2xy/3x is a negative integer

 Option B: x-y is a positive integer

 Option C: (-x

 Option D: x/y is a negative integer

 Option E: 2x+y is a negative integer
[A]: Option C


[Q]: Question: A car has been driven with an average speed of 30 kilometers per hour during the first 30 kilometers of a journey. Upon reaching the 30th kilometer, the car then travels at 45 kilometers per hour for the next 30 kilometers. Find out the average speed of the car if it has not been stopped at all during the journey.

 Option A:  35

 Option B:  36

 Option C:  37.5

 Option D:  38

 Option E:  40
[A]:
Option B