GWD 21-21

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21(1184)
            Which of the following most logically completes the passage?

 

Mastitis is an infection of the udder in cows that, although not dangerous, causes them to give poor-quality milk.  Most cases of mastitis are caused by the bacterium Staphylococcus aureus, against which antibiotics are ineffective.  However, a related bacterium, Staphylococcus simulans, quickly clears up even severe infections of S. aureus simply by displacing the bacteria.  S. simulans is nevertheless unlikely to become the preferred treatment for cases of mastitis, since ______

	A.certain dangerous bacteria that normally cannot take hold can do so in the presence of S. simulans
	B.the current resistance of S. aureus to antibiotics derives in part from a past pattern of overuse of those antibiotics
	C.the milk from cows infected with S. aureus is generally not of such poor quality as to be entirely unusable
	D.careful farming practice can reduce the incidence of mastitis to a minimum
	E.the only symptom of mild cases of mastitis is the deterioration in the quality of the milk produced

这题为什么选A阿？A是什么意思呢？

lysun

A大概意思是：一种非常危险的特定细菌，一般情况下不会感染，但是有S. simulans 的时候，牛会感染这种病毒。

因为Staphylococcus aureus只是影响牛奶质量，而这个特定细菌却非常危险，所以如果用S. simulans来控制Staphylococcus aureus会得不尝失。

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