Here's a problem to solve: A group of science students used water, filter paper, and a hot plate to separate a mixture of salt and sand. Which of the following did the students most likely do first?

Among the 4 following options, which is the correct answer?

- A: shake the mixture until the sand settles on the bottom
 
- B: pour the mixture through the filter paper
 
- C: heat the mixture on the hot plate
 
- D: dissolve the salt by adding water to the mixture
 