Evolution occurs by, the process in which
some members of a species, being better suited or adapted to their
environment, produce more offspring than others, so they pass
“advantageous traits" to their offspring,

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

the correct answer is b

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