I do not know but thanks fir asking g
Answer:
Because people found an extra source of energy with an incredible capacity for work.
B. Interactions between humans and the environment< i guess
Answer:
True!
Explanation:
One form of secret writing used by both the British and American armies was invisible ink. During the Revolutionary War invisible ink usually consisted of a mixture of ferrous sulfate and water. The secret writing was placed between the lines of an innocent letter and could be discerned by treating the letter with heat or a chemical substance. The recipient placed the paper over the flame of a candle or treated it with a chemical reagent, such as sodium carbonate, which would reveal the letter’s hidden contents.