第24题: [单项选择]The meeting was so prolonged and exhausting that ______ the speakers stopped for refreshments. A. at ease B. at random C. at intervals D. at large 参考答案:C 答案解析:此题考查作状语用的介词短语。C项at intervals意为“不时地”,介词和名词间可插入形容词,如:at long intervals偶尔;at short intervals频频; at regu