单项选择题

Apart from their ability to (21) themselves to varying climate conditions, rats possess another (22) that gives them an advantage in extending their boundaries. More so than most other animals, (23) snakes, mosquitoes and spiders, they induce fear. Why should this be so Certainly they carry (24) and man is slow to forget the Black Plague (25) killed off millions of people in the fourteenth century. Also, rats have been known to bite (26) babies, but the number of such attacks is very much exaggerated. One reads (27) the danger of being attacked by "a cornered rat", but this belongs to fiction; rats do not (28a) your throat, as many would have us believe. (29) , it is difficult to believe that its appearance can be a source of (30) ; the common black or brown rat can almost be regarded as a frightful creature while its cousin, the squirrel, is quite pretty and gentle.

29()

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