Explanation and analysis: The topic is a brain teaser, in which the question is "Why is the sea blue". This is because there are fish in the sea, and fish in the sea spit bubbles. When spitting bubbles, the onomatopoeia word is "Yilulu, Yilulu" and the English word is blue, so there are fish spitting bubbles in the sea.

Extended data:

Think about solving problems:

When thinking encounters special obstacles, we should quickly leave the habit of thinking and think about problems from other aspects, such as:

Mom and dad, son and daughter, as well as the housekeeper and dog, go for an outing together. When they reach the river, they must go to the other side. There is only one boat. When mom is away, dad beats his daughter. When mom is away, mom beats her son. Dogs will bite when the housekeeper is away! Excuse me: how should they go?

If you think too much about how to live, or cling to the question of who is with whom, you will be completely confused by the topic, and the answer is to change the way.