Answer: Second option is correct.
Explanation:
As we know that
when a straight line is cut by a transversal or any other line.
It divides the straight line into two angles.
And the sum of two angles becomes supplementary.
And this pair of angle is known as "Linear pair".
So, ∠3 and ∠4 are linear pair and ∠3+∠4=180°.
Hence, Second option is correct.