Answer:
a. a║b
b. c║d
c. AB║CD
d. none
Step-by-step explanation:
a. If distinct lines in a plane are perpendicular to the same line, then they are parallel.
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b. If same-side interior angles are supplementary where a transversal crosses two lines in the same plane, then those two lines are parallel.
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c. If alternate interior angles are congruent where a transversal crosses two lines in the same plane, then those two lines are parallel. (Here, the measure of the upper angle at A is 180°-78°-67° = 35°, congruent with the lower angle at C. Those two angles are alternate interior angles with respect to lines AB and CD and transversal AC.)
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d. The marked angles are unrelated to each other, so define nothing about the relationship between lines a and b, or between lines c and d. However, they do mean that if a║b, then c║d.
