Hosea Is Studying the Relationship Between Caffeine Consumption and Problem-Solving

Hosea is studying the relationship between caffeine consumption and problem-solving ability. Which of the following is a quantitative way to operationalize problem-solving ability?

A) The time spent solving a math problem
B) The type of puzzle solved (Sudoku puzzle or a crossword puzzle)
C) Whether participants used insight or trial-and-error techniques to solve the problem
D) The report of a teacher about whether a student is a good or bad problem solver