Given the task definition and input, reply with output. You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

A scientist was observing a unicellular organism over a period of time. He noticed that vacuoles kept moving to the same place in the plasma membrane to empty their contents outside the cell. Which organism was he observing?
(A) amoeba (B) euglena (C) paramecium (D) volvox
C