Scientists use the theory of plate tectonics to understand the reasons volcanoes develop in certain locations. How does this show the validity of the theory?

A. The scientists are using observations.
B. The scientists are making predictions.
C. The scientists can see the plates moving beneath the volcano.
D. The scientists are repeating the experiments .

Astudent pours 10.0 g of salt into a container of water and observes the amount of time it takes for the salt to dissolve. she then repeats the process using the same amounts of salt and water but this time she slowly stirs the mixture while it is dissolving. the student performs the experiment one more time but this time she stirs the mixture rapidly. the dependent variable in this experiment is: time for salt to dissolve speed of stirring amount of water mass of salt