Replacing Words with Synonyms​

he knows mathematics much better than he did last year.he must   work a lot in summer.2.your mathematics is very poor.you must to work at it in summer.3.where is peter? -oh,he must read in the library.he is getting ready for a very difficult examination.4.you must to study english for several years already.your language is very good.5.oh,look how white and clean everything is! it must to snow at night.6.oh,you are all in snow,you look like a snowman.it must   snow heavily.7.look,what huge snowdrefts yhere are everywhere,and the path is covered with knee-deep snow.it must to snow for several hours already.8.you look fresh! you must   have a good sleep at night.9.9you look very tired.you must have a good sleep at night