Answer:
B. a ⊥ d
Step-by-step explanation:
If lines "a" and "d" are in the same plane, they are perpendicular to each other. If not, there is no relationship between the lines.
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Lines parallel to the same line are parallel to each other, so a║c. In the same plane, a line perpendicular to one of two parallel lines is also perpendicular to the other. (For example, one side of a rectangle is perpendicular to both of the adjacent sides, which are parallel to each other.)
The appropriate choice is ...
a ⊥ d
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In 3 dimensions, ...
Consider a cube. A given edge will be perpendicular to both of the two edges it meets at a corner.
It will not intersect (has no "perpendicular" relationship to) either of the edges parallel to those that meet at the corner at the other end of the space diagonal.
