Task: Question Generation
Input (English): Background Paragraph: Active transport occurs when a substance passes through the cell membrane with the help of extra energy. This happens when a substance moves from an area where it is less concentrated to an area where it is more concentrated. This is the opposite of diffusion. The substance moves up, instead of down, the concentration gradient. Like rolling a ball uphill, this requires an input of energy. The energy comes from the molecule named ATP (adenosine triphosphate). The energy allows special transport proteins called pumps to move substances to areas of higher concentration. An example is the sodium-potassium pump. 
Story: John is trying to figure out how substance passes through the cell membrane. He noticed two different cases, case A and case B. In case A active transport is involved, but in case B diffusion is involved. He needs to do further study to learn about the details of these processes.
Output (English): In which case the substance moves down the concentration gradient, case A or case B?