第33题: [单项选择]The research scientists often meet with problems_____new types of instrument for their solution. A. requiring B. required C. to require D. being required 参考答案:A 答案解析:此题应选现在分词requiring,在句中作定语,修饰problems,相当于定语从句…problems which require...,因为它们在逻辑上是主动关系,所以应选现在分词。句意为:“科研