Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: Water is the "life blood" of our earth. It is in every living thing. It is in the air. It runs through mountains and valleys. It forms lakes and oceans. Water is everywhere. Nature has a great water system. Rain water finds its way to streams and the oceans. Here at the mouth of a river there is much important plant and animal life. Pollution destroys this life, so we have to clean out streams and rivers. Man has to work with nature--not against it.
Answer: blood
Output:
According to the passage, water is the _ of our earth.