The correct answer is D. Flatworms
Step-by-step explanation:
In biology, a flame cell is a cell found in organisms that are both simple or primitive and invertebrates, for example, Nemertea or ribbon worms and flatworms. The flame cell is the one that works as an excretory system for the organism mainly by removing or excreting substances that are not used by the animal. Additionally, this cell contains a flagellum and a special tube cell that is designed to be an excreting system. Considering this, it can be concluded flame cells are found in flatworms.