Which of the following can be disposed of in the sink?

A) saliva
B) blood
C) salt solution
D) preservative

Salt solution (assuming it is not a hazardous chemical) can typically be safely disposed of down the sink as it is a dilute solution that will not harm plumbing or the environment. Saliva should be disposed of in a biohazard container, blood should be disposed of in a regulated medical waste container, and preservatives may contain hazardous chemicals that should not be dumped down the sink.