A chemist added hydrochloric acid to a sample of baking soda in a beaker. Immediately, the mixture of the two chemicals began to fizz and bubble. Which of the following observations about the fizzing mixture provides evidence of a chemical reaction?

A. The temperature of the beaker did not change.

B. A substance escaped from the beaker in the form of a gas.

C. Some of the baking soda remained in the bottom of the beaker.

D. Most of the baking soda appeared to dissolve in the acid.