Which of the following best completes this definition?

Question

Two lines are parallel if and only if ______________.

A.
they intersect and form acute angles

B.
they do not lie in the same plane and do not intersect

C.
they intersect and form right angles

D.
they lie in the same plane and do not intersect

Answer 1

The best option that completes the definition is:

D. they lie in the same plane and do not intersect

So the complete definition would read: Two lines are parallel if and only if they lie in the same plane and do not intersect.