A. INHABIT B. LIVE C. STAY D. EXIST PASSAGE B

50.

A. inhabit

B. live C. stay

D. exist

Passage B:

Researchers have been perplexed by the increasing prevalence of allergies in children. While many (51)

______ appear to contribute to the (52) ______ of allergies, sensitization to common allergens has been

shown to reduce the risk of allergies persisting from childhood into adulthood. For example, one recent

study shows that exposure early in life to cats and dogs may protect children against allergies (53) ______

pets, dust mites, ragweed, and grass, among other things. Some allergists had (54) ______ thought that

repeated exposure to pets in infancy would (55) ______ the likelihood of developing pet allergies.

(56)______, it is now believed that endotoxins, substances (57) ______ in the mouths of cats and dogs,

may (58) ______ help to prevent allergies. When a pet licks a child during play, endotoxins are transferred

from the animal’s tongue to the child. Endotoxins are (59) ______ to help the human immune system (60)

______ resistance towards some allergens in the environment. The bottom line is that living too clean a life

may contribute to the increasing number of children with allergies.