第29题: [单项选择]However ______ certain natural resources may be, they cannot reproduce themselves and are bound to be used up ultimately. A. abundant B. adequate C. sufficient D. satisfactory 参考答案:A 答案解析:题意是:不管某些自然资源多么______,但它们不能自我再生,最终仍会耗尽。[A]abundant“充裕的,丰富的”,符合题意。[B]adequate“足够的,适当的”,[C] sufficient“