Answer:
C. She treats the coral samples identically with varying levels of carbonic acid.
Explanation:
She releases cement particles into a random number of the coral samples.
Doing this is uncontrolled, using a random number for anything in an experiment is a no no.
She uses three different types of coral to establish her dependent variables.
Different types of coral could react differently to the acid, always use only one dependent variable in an experiment.
She obtains her coral samples from coral reefs surrounding different continents.
It is important that the samples of coral be as close to the same as possible so that the coral variables stay constant.
