You are given a mathematical question described with an open-ended vocabulary. Questions in this task involve real-world situations, describing a mathematical problem. You are also given 4 or 5 answer options (associated with "A", "B", "C", "D", "E"). Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D', 'E'. LaTeX mathematical format (the standard way to express mathematical expressions in the typesetting software known as LaTeX) is used to express equations. Each question is solvable with high school math knowledge. Give only one answer for each question.

Max purchased some shares of stock at \$10 per share. Six months later the stock was worth \$20 per share. What was the percent increase in the value of Max' s investment?
(A)20\% (B)50\% (C)100\% (D)200\% (E)500\%
C