Answer:
It begins a list of how mucus keeps us healthy.
Explanation:
The sentence shown in the question above is a bridge to the subject addressed in the second paragraph, which is how mucus makes us healthy.
Although it seems disgusting, mucus is very important in our body, serving as a protective barrier that prevents our body from being invaded by bacteria and other microorganisms that can cause problems of different intensities. This is shown in the second paragraph.
Answer:
The Answer would be A, or 1, It begins a list of how mucus keeps us healthy.
Explanation: Hope this helps!