Task: Question Answering
Input (English): Problem: at their respective rates, pump a, b, and c can fulfill an empty tank, or pump - out the full tank in 2, 3, and 6 hours. if a and b are used to pump - out water from the half - full tank, while c is used to fill water into the tank, in how many hours, the tank will be empty ?
Options: a. 2 / 3, b. 1, c. 3 / 4, d. 3 / 2, e. 2
Output (English): c