What's paraldehyde? How is it prepared?

Which function is performed by earths atmosphere? a. ultraviolet rays are prevented from reaching the ozone layer. b. earths temperature is raised and moderated by trapping in heat c. charged particles from the sun are prevented from reaching earth. d. magnetic charges from space are prevented from reaching earths surface.

Each pair of clay balls represents to planetesimals if each plane test molluscum pound of the same material and is separated by the same distance which pair experiences the greatest gravitational attraction

What is an example of a physical property?