Improved nutrition, medical treatment, and sanitation all account for the dramatic increase in in the twentieth century. a. the life expectancy crossover b. functional age c. active living age d. average life expectancy

that is wrong, its not thymus.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds