(2013·吉林长春高中毕业班第一次调研)As the immune system weakens, it loses the ability illnesses.
A. fighting
B. fought
C. to fight
D. to be fought
网友回答
A. fighting
B. fought
(答案→)C. to fight
D. to be fought
解析：C 考查非谓语动词。句意：由于免疫系统衰退，它失去了与疾病抗争的能力。表示“……的能力”，要用不定式作后置定语来修饰the ability。