Which of the following is not a natural source of light?
a. oil lamps
b. the sun
c. phosphorescence
d. fluorescence

Disinfection of impression materials is usually accomplished by a. sterilization with high heat. b. spray or immersion in a chemical disinfectant. c. sterilization with steam under pressure. d. allowing the impression to sit 24 hours in water until all the organisms die.

What is hydroelectric power produced by?

Creating new things to solve problems and improve life depends on the close interaction of which two fields?