Q:Answer the following question given this paragraph: 41.3 Excretion Systems Many systems have evolved for excreting wastes that are simpler than the kidney and urinary systems of vertebrate animals. The simplest system is that of contractile vacuoles present in microorganisms. Flame cells and nephridia in worms perform excretory functions and maintain osmotic balance. Some insects have evolved Malpighian tubules to excrete wastes and maintain osmotic balance. Q: The simplest system is that of contractile vacuoles present in what? Choices: - parasites - macroorganisms - crystals - microorganisms A:
A:
microorganisms