Answer:
The correct option is: b. sulcus
Step-by-step explanation:
Gingival sulcus refers to the shallow space present between the tooth and the gum tissue, called the gingival margin that surrounds the tooth.
The depth of the healthy gingival sulcus is about three millimeters and it is readily self-cleansable. The gingival sulcus is lined by the sulcular epithelium.