You will be given a definition of a task first, then some input of the task.
In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").

a force acting on an object in the opposite direction that the object is moving can cause that object 's speed to decrease in what motion? (A) frontward (B) backward (C) downward (D) upward
Output:
A