Which of the following is an example of an open system?
a) an aquarium with both plants and animals
b) an enzyme found in deep ocean organisms that allows them to glow
c) a living single-celled organism such as phytoplankton
d) a river that has been dammed

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

u can get stuck if wrong may u pls give mt the optians

explanation: