Which of these statements is true?
a. chemical reactions can be slowed down by increasing the temperature.
b. once a chemical reaction gets started, the reacting particles no longer have to collide for products to form.
c. enzymes are biological catalysts.

Ms. sullivan's class is designing a miniature roller coaster. after first setting it up, they find that it didn't have enough speed to go through the loop de loop. instead of taking out the loop, they decide to increase the height of the first hill the coaster goes down, and this adds the speed needed to make it through the loop. what would be a drawback to this plan in real life? a) no one likes loop de loops. b) there is no downside to this plan. c) a higher hill means a scarier ride. d) a higher hill takes more time and material to build.