If two parallel lines are intersected by a transversal, then which of the options below is necessarily true?
1
The sum of the measures of a pair of alternate interior angles is 180°
2
The sum of the measures of a pair of corresponding angles is 180°
3
The sum of the measures of a pair of interior angles on the same side of the transversal is 180°
4
The sum of the measures of a pair of vertically opposite angles is 180°