Answer:
4) It suggests there is one final point to discuss regarding mucus.
Explanation:
The word "Furthermore" indicates that there is still a point about the mucus that needs to be discussed before the article is finished. This point is probably related to other characteristics of the mucus, besides the impression of unpleasant goo. This point that will still be discussed will be about the beneficial functions of mucus in our organism, in addition to showing its importance for our health.
Transitions help connect ideas, so the second option would be your answer.
Hope I helped!
