Task: Question Answering
Input (English): Felicia investigated whether water color affected how fast the water heated in sunlight. She poured tap water into five beakers and placed food coloring in four out of the five beakers. Felicia then used a thermometer to measure the temperature of the water in each of the beakers. Which of these was used as control in her investigation?  
 (A) mixing the food coloring in water (B) testing the beaker of uncolored tap water (C) using the same amount of water in each trial (D) testing the colored water samples at different times
Output (English): B