Which substance is a greenhouse gas that is emitted by human activities, is the most widespread, and remains in the air the longest? vapor
methane
fluorinated gas
carbon dioxide

Embryos of different species look very similar, which shows that the organisms share a ancestor.

Joseph has hypothesized that sound travels in waves. if he were following the scientific method, what should he do next? a. ask a question. b. test the hypothesis. c. study the results. d. tell other scientists about his hypothesis.

What is the maximum number of electrons that an atomic orbital can contain?