Need help quick!! Please explain how you got your answer.

Multiplying an even number of negative numbers gives an answer that is choose from:

Consider the proof. given: segment ab is parallel to line de. prove: what is the missing statement in step 5?

Use stokes' theorem to evaluate c f · dr where c is oriented counterclockwise as viewed from above. f(x, y, z) = xyi + 5zj + 7yk, c is the curve of intersection of the plane x + z = 8 and the cylinder x2 + y2 = 81.