Which of the lines, if any, are parallel

a and c are parallel.

Step-by-step explanation:

Let's find slope for each line.

If slopes of lines are same then they are parallel.

for line described by a : slope = = 1

For line b slope = = 2

For line c slope = =1

So slope of lines a and c are same. a and c are parallel to each other.

(a) the volume of the cone is 20/3 in3

hence, option a is correct.