根据句意和首字母，写出各单词的正确形式。
The teacher says I have to learn grammar again because I always make m ___ in grammar.
Much of the village is c        by snow.
This problem is very difficult. He can not solve it e_______.
You will fail your next exam u________ you start to work at your studies now.
I think he will work out the problem, because he is quite a p         person.