Which material undergoes radioactive decay? all elements that have a half-life all elements that contain atoms with protons all elements that have turned into a new element all elements that have a consistent number of particles

Using complete sentences, describe the central economic problem facing all humans. why does this require people to make choices? how can this result in opportunity costs?

Which of the following is evidence to the past existence of glaciers?

Which phrases describe oxygen's roles in earth’s atmosphere? check all that apply. allows fuels to burn forms clouds that produce rain is the gas that animals breathe is used by plants to produce food forms ozone that absorbs the sun's harmful rays