1.Why do engineers put up power lines so that they are slack in hot weather?
(slack as in like slacking down)

2.Why are some bridges supported at one end by rollers?

3.Why are the bolts that hold steel rails together in oval holes?

4.Why are there gaps between adjoining rails?

thanks for you help. i’ve order prescription drugs done some of them but i’m not sure about the bridge and rollers one.
and i want to make sure this is right so i can get off to a good start for the semester. if i get an A on my paper all put you as best answer
forgot a question

6.What is the of a gap in the road of a bridge?