請問呢兩句sentences有咩錯誤之處?

1. writting --> writing
2. All.... can not = not all 不是全部
= not all students can answer the difficult question. (but some can)
全部都唔識應該寫：
No student can answer that difficult question.

1) Mary is writing a postcard to her cousin.
2) All students cannot answer the difficult question.

1writing (wrong spelling)
2 cannot is one word

2007-08-23 11:08:16 補充：
1. write.....writing...wrote.......written