Hey there!
Your answer is D. salt water Â
A mixture has more than one substance.
Salt water is made up of multiple different substances, salt (NaCl) and water (Hâ‚‚O).
Carbon dioxide (COâ‚‚), water vapor (Hâ‚‚O), and oxygen gas (Oâ‚‚) are each just one substance.
Hope this helps!