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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
好像GWD的后半部分都很阴，即使看了答案、看了解释，也是一头雾水，完全没有之前做完很通气的感觉：（
这题为什么是A？完全找不到北 | 
