a) Parallel lines have the same slope. 5 and 1/5 are not equal, so they are not parallel.
b) Perpendicular lines have negative reciprocal slopes. That means when you multiply the slopes together, you get -1. Let's try our slopes. 5 * 1/5 = 1, not -1, so these slopes are not negative reciprocals, and the lines are not perpendicular.
c) A vertical line has undefined slope since the slope of a vertical line involves division by zero. Here, the two lines have well defined slopes. The lines are not vertical.
d) This is the only choice left, so it is the answer.
