1、The letter they were looking forward to _________ at last。 A. arrived B. arriving C. had arrived D. arrive 对于此题，基础稍差的同学可能选D，认为空格前的 to 是不定式符号，所以后接动词原形；基础稍好的同学可能会选B，知道 look forward to 是短语，意为 look...