【简答题】当对关系R和S使用自然连接时,要求R和S含有一个或多个共有的 。
【判断题】中央银行提高再贴现率会导致货币供给量的减少和利息率的提高。()
【判断题】I don't know why I had a headache.
【判断题】I don't know why I had a headache.
【判断题】铁路篷布因托收货人责任损坏、丢失时,自指定送回车站之日起,至赔偿当日止,按规定核收篷布延期使用费。
【简答题】I don't know why he isn't here.
【单选题】I don't know why I______.