1.The four young faces on which the firelight shone brightened at the cheerful words...

【难句解析】这句的主干是...faces...brighted...，on which引导的定语从句修饰faces，后面的动词darkened的主语也是faces

【句子翻译】这句令人愉快的话使炉火映照下的四张年轻的脸庞明亮起来

2.You know the reason Mother proposed not having any presents this Christmas was because it is going to be a hard winter for everyone...

【难句解析】这句的主干是you know the reason...was...，其中的Mother... Christmas做定语修饰reason

【句子翻译】你们知道妈妈为什么建议今年圣诞节不派礼物吗？因为寒冷的冬天就要来了...