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: The ratio of a to b to c is 2 to 3 to 4, and a, b, c are positive integers. If the average (arithmetic mean) of the three numbers is 36, what is the value of a?

Option A: 21

Option B: 24

Option C: 25

Option D: 27

Option E: 30
[A]: Option B

[Q]: Question: In what time will a train 200 m long cross an electric pole, it its speed be 144 km/hr?

Option A: 2.5 sec

Option B: 2.9 sec

Option C: 3.5 sec

Option D: 7.5 sec

Option E: 5 sec
[A]: Option E

[Q]: Question: what is average of 2000 terms of the given series
1,-3,2,-4,3,-5,4,....

Option A: 1

Option B: 0.5

Option C: -0.5

Option D: -1

Option E: -2
[A]:
Option D