Mammals evolved into larger organisms and began subdividing into various species in the a. mesozoic era c. cenozoic era b. paleozoic era d. devonian era

this is math not biology xd

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