Answer:
D. a║b, because if two lines are perpendicular to the same line, then they are parallel to each other.
Step-by-step explanation:
This is more of a rule than anything else, but to prove this, you can think of c as the transversal. The 4 angles at the intersection of line a and line c are 90 degrees, and so are the 4 angles at the intersection of line b and line c. Using the converses of the Corresponding Angles Theorem, Same Side Interior Angles Theorem, Alternate Interior Angles Theorem, etc.., you can prove that a and b are parallel.
