Which of the following two are the major constituents of Bio-gas ?

1. Methane
2. Butane
3. Carbon dioxide
4. Carbon monoxide

Select the correct answer from the code given below :
Code:

A) 1 and 3

B) 3 and 4

C) 2 and 3

D) 1 and 2

This MCQ is part of the UP PSC Previous Year Questions (PYQs) series, focusing on UPPSC Prelims 2025 (GS Paper I)