Question

warts are local growths on the skin that are caused by
a. a virus
b. a yeast.
c. a fungus
d. a bacterium

Explanation:

疣是由人乳头瘤病毒（HPV）感染引起的皮肤表面良性赘生物。酵母是真菌的一种，真菌、细菌都不是引起疣的原因。

Answer:

A. a virus