Questions

(a) refers to political importance and (b) to economic importance. Out of (c) and (d), (c) is more important.

Salivary glands of man are  3 pairs = 6. They are one pair of parotid glands, one pair of sub-maxillary or sub-mandibular glands and one pair of sub-lingual glands.

Epiglottis is that prevents food from entering the windpipe. 

It is a cartilageous flap that flaps opens and closes when swallowing. When you swallow, the epiglottis flattens backward to cover the entrance to your larynx and prevent food from entering the lungs and windpipe. The epiglottis returns to its usual position after swallowing.