Task: Question Answering
Input (English): Problem: if a 1 mm thick paper is folded so that the area is halved at every fold, then what would be the thickness of the pile after 50 folds ?
Options: ['a. 100 km', 'b. 1000 km', 'c. 1 million km', 'd. 1 billion km', 'e. none']
Output (English): d