Mark has diabetes and needs to undergo dialysis twice a week. Dialysis purifies the blood by removing waste and excess water from the blood. Which body system does dialysis perform a function for?

excretory system

Explanation:

The excretory system's job is to remove waste and excess water from the blood.  Since Mark has diabetes and his body can't naturally do that, he has to undergo dialysis.  Dialysis helps the kidneys function.  And the kidneys are part of the excretory system.

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that would be the steamboat because none of the other things are forms of transportation