单选题 His theories were so ______ that few could see what he was trying to establish.
A. logical B. scholarly C. theoretical D. vague

【正确答案】 D
【答案解析】(vague含糊的)。句意为：他的理论含糊不清，很少有人明白他想证实什么。 A．logical合乎逻辑的；B．scholarly博学的，好学的；C．theoretical理论上的。