You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Sometimes two air masses stop moving when they meet. These stalled air masses create a stationary front . Such a front may bring clouds and precipitation to the same area for many days. Answer: stationary front
Output:
What weather phenomenon, which may bring clouds and precipitation, is created by stalled air masses?