Answer:
<2≅<6.
Step-by-step explanation:
Two lines are parallel if their corresponding angles are equal.
The other options that is <1≅<3 and <7≅<5 are pair of vertical angles .These are not necessary conditions for the lines to be parallel.
In the figure given <2 and <6 are corresponding angles for lines a and b.
If the measure of these angles are equal the lines a and b will be parallel.
The first option that is <2≅<6 will make the lines parallel.
