Task: Question Answering
Input (English): A student investigates the effects of fertilizer on corn plants by performing the following steps.1. Plant groups of corn plants in the same type and amount of soil in full sunlight.2. Add the same amount of different brands of fertilizer to each group.3. Water the plants for 5 minutes each day.4. Measure the heights of the plants each day. What is the independent variable in this investigation?  
 (A) type of plant (B) height of plant (C) amount of fertilizer (D) type of fertilizer
Output (English): D