C. If the algae made the sea turtles sick, then removal from the water and treatment would make them healthy.
Looking at the description of the situation, Shenita hypothesized that sea turtles were affected by toxins from a recent red tide event. So she removed them from the contaminate environment and treated them with a drug to counteract the red tide toxins. And the way things turned out, her hypothesis looked correct. With that in mind, let's look at the options and pick the correct one.
A. If the water is dirty, then it would make the sea turtles die.
* This is a possibility, but it's rather generic and not specific to the situation Shenita observed. So this is a bad choice.
B. If the chemicals in the water made the sea turtles sick, then filtering the water would make them healthy.
* This is also true. But Shenita didn't do any water filtering and this doesn't apply to the observed situation. So another bad choice.
C. If the algae made the sea turtles sick, then removal from the water and treatment would make them healthy.
* This pretty much describes what happened. So this is the correct choice.
D. If the sea turtles are in clear ocean water, then they should go to the mote marine lab.
*This doesn't describe the situation, so it's a bad choice.