You are given a passage. You need to construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) its answer is the whole paragraph. Avoid creating questions that can be answered correctly without actually understanding the paragraph.
Q: The 4 mm probably refers to the depth of your gum pockets (the space betwen the top of your gums to the alveolar bone that holds your teeth. Your dentist would measure this with a probe.

If your pockets are deeper than 4 mm then it means that you have had bone loss which is usually caused by periodontal disease (an infection in the gums). The best way to prevent periodontal problems is to brush and FLOSS your teeth regularly (brush at least twice a day for two minutes).

I emphasize flossing, because often people don't realize just how important it is. The contact between the two teeth are where food are most likely to get stuck, and therefore where bacteria sticks most often, too. The purpose of flossing is to really clean that surface where two teeth touch. So instead of focusing on just making the floss go down between the teeth, you want to follow the sides of your teeth to make sure you remove the plaque. So you should be going up and down two to three times along the tooth on both sides of the contact.

Hope this helps!
A:
Where is the gum?