The diagrams show the four primary steps in the production of work in a four-stroke heat engine.

what is the correct order in which these steps occur?

y, w, x, z
x, z, w, y
w, x, y, z
z, x, y, w

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.