Which of these is an example of a chemical change?
a. burning a piece of wood
b. breaking a tree branch
c. dissolving salt in water
d. melting water

Amino acids contain the elements carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. of the 20 amino acids found in humans, 11 are called "nonessential" because they can be manufactured by the body when needed. which elements in these 11 amino acids are commonly obtained from the metabolism of sugar molecules?

Which of these has happened to your food by the time it reaches your small intestine? a. all the macromolecules have been broken down completely. b. lipids and starches have been partially broken down. c. starches and proteins have been partially broken down. d. proteins and lipids have been broken down into subunits.

How much time has elapsed from the very beginning of "the memior of the conquistador bernal diaz del castillo" to the end? a. castillo's whole life b. a quarter of an hour c. a few weeks d. a decade