Two lines intersect at a point, forming ​ ∠1 , ∠2 , ∠3 , and​ ​ ∠4 ​ . ∠1 and ∠3 are vertical angles. ∠2 and​ ​ ∠4 are vertical angles. m∠1=70° What is the measure of ​​ ∠2 ​?
20°
70°
90°
110°