A Graph A
B. Graph B
C. Graph C
D. Graph D

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

the answer is d p: cell, q: organ, r: organ system, s: tissue

yes, because even though a theory has a  lot of evidence to support it, it is not always true