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: Given that there are 6 basketball players per team, how many ways can you select 2 basketball players from 3 teams if no more than one player can be selected from each team?

 Option A:  15

 Option B:  30

 Option C:  60

 Option D:  108

 Option E:  90
[A]: Option D


[Q]: Question: A and B together can complete a work in 12 days. A alone complete it in 20 days. If B does the work only for half a day daily, then in how many days A and B together will complete the work?

 Option A: 110 days

 Option B: 11 days

 Option C: 15 days

 Option D: 20 days

 Option E: 17 days
[A]:
Option C