Marissa is testing a hypothesis through experimentation. she believes that immersing ocean coral in carbonic acid will slow the coral’s growth. which of these actions will prevent marissa from introducing confounding variables into her experiment?

The answer choices to this question are:

A) She releases cement particles into a random number of the coral samples.
B) She uses three different types of coral to establish her dependent variables.
C) She treats the coral samples identically with varying levels of carbonic acid.
D) She obtains her coral samples from coral reefs surrounding different continents.

Best Answer is: 

A) She releases cement particles into a random number of the coral samples.

Theory:
It has been researched that ocean acidification caused by carbon dioxide emissions causes a decrement in the coral reef growth and this will keep slowing down unless steep and rapid reductions in greenhouse gas emissions are made. And the Coral reefs offered economic opportunities would advantage the surrounding communities from fishing and tourism.