[解析]
56.when;考查定语从句,在这个定语从句中先行词the time 指时间,故用关系副词when.
57.sending;考查非谓语动词,by是介词,后面要跟名词或名词性短语,故用动名词形式sending.
58.exactly;考查副词,此处用副词作状语修饰整个句子.
59.It;考查固定句型,It is said that…是固定句式结构,意为"据说…".
60.that;考查固定句型,It is believed that…是固定句式结构,意为"据认为…",it作形式主语,that从句是真正的主语.
61.is celebrated;考查动词的语态,主语Valentine's Day 与动词 celebrate是动宾关系,故用被动语态is celebrated.
62.to;考查固定短语,此处用介词to与前面的from构成短语"from…to…",意为"从…到…".
63.unfortunate;考查形容词,此处用形容词作定语修饰后面的名词men,根据后面的定语从句who received nothing 可知要用否定形式unfortunate.
64.on;考查介词,具体到"在某一天"要用介词on.
65.in;考查介词,in这里指"在某一方面",play a part in doing是固定搭配,意为"在…方面起作用".