What causes different colors to appear in the sky? the absorption of light by air molecules
the reflection of light by bodies of water
the greenhouse effect in Earth’s atmosphere
the scattering and reflection of light by dust particles

In which research method does a researcher change the value of one variable to determine how the change affects another variable? a. experiment b. observational research c. survey d. case study

Martin, a 32-year-old human relations administrator at a university, believes that all professors over age 50 are incapable of learning the new educational technologies and are content to keep presenting their same "tired, boring" lectures. he often expresses these views to other administrators and does not encourage any of the "older" faculty members to attend professional development meetings related to new teaching approaches nor does he suggest that the university send them to any of the technology conferences. martin is exhibiting

As of 2013, the world’s total population was about