Every student should do his own homework.英语,语法

Every student should do his own homework.英语,语法
Every student should do his own homework请问此句型中OWN 可以省略掉吗
I like to receive letters but do not like to write them。还有此句子能否省略掉“them”,有知道的朋友请详细解答下，
London is much hotter in summer than my hometown.请问这个句型为什么不正确

第一个句子：own可以省略,从语法上没有问题,此时加上在句意上有所强调
第二个句子：这个是代词的用法,原句其实是I like to receive letters but do not like to write letters.在英语中避免重复,所以第二个letters 用them替代了
第三个句子：这里比较的是气候,天气一般用It 代替,所以句子主语不能用London.这句话应该是It is much hotter in London in summer than in my hometown.（用it代表气候,天气等.）