Answer:
"They add up to 180 degrees, because they are a pair of supplementary angles"
Step-by-step explanation:
When parallel lines are cut by transversal, it creates vertical angles (opposite of each other) that are equal AND also supplementary angles (that are adjacent to each other and fall in one line). They add up to 180 degrees.
Looking at the figure, we see angle 1 and 2 fall in one line which is 180 degrees. Thus, angles 1 and 2 are supplementary, they add up to 180 degrees.
The correct choice is "They add up to 180 degrees, because they are a pair of supplementary angles"
