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.

Input: Consider Input: 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

Output: Option D


Input: Consider Input: Question: A is twice as fast as B. If B alone can do a piece of work in 18 days, in what time can A and B together complete the work?

 Option A: 10

 Option B: 16

 Option C: 18

 Option D: 6

 Option E: 12

Output: Option D


Input: Consider Input: Question: Four people are on an elevator that stops at exactly 4 floors. What is the probability that exactly one person will push the button for each floor?

 Option A: 4!/4^4

 Option B: 4^4/4!

 Option C: 4/4!

 Option D: 4/4^4

 Option E: 1/4^4


Output: Option A