What is his error by checking his work

What does the process of natural selection involve

Agas can holds 2.0 gal of gasoline. what is this quantity in cubic centimeters?

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?