check pls

1.Do not open the door to stangers. They may be dangerous.
In written English, try not to use abbreviated forms like don't, can't, won't, isn't. Always use the complete format such as do not, cannot, etc.

2. How to prevent tooth-decay?
In this case "tooth-decay" is used as a noun.

3. Do not litter. Use the rubbish bin.
Try to keep your sentence simple and short. Again, avoid abbreviations.

4.The sun is bright. Let us sit under the shade.
In this sentence the word "shade" is used as a noun to replace "shady tree"

5. l like collecting stamps.
Collecting (收集) is a habbit / hobby. Gathering (集合) is simply an action.

6. My cosin had a fever yesterday.
Nothing wrong here.
在英文文法中, 有 " ' "的(eg. it's)是 "is"的簡寫. 同無 " ' " (eg. its)是不同.
it's = it is 它是, its = 它的

2007-06-20 17:51:08 補充：
睇少左! 在(6)中, cosin正確是cousin

1. Do not open door to strangers! It may put you in danger.( it may not be safe).

2. How to prevent tooth decay?

3. Do not litter, please leave garbage in the trash can.

4. It is too sunny, it may be better to sit under the shade.

5. I like to collect stamps.

6. My cousin had a fever yesterday.

I assume that you are trying to check for grammatical mistakes and typos?

1.Don't open the door to strangers, they're dangerous.
2.How do you prevent teeth from decaying?
3.Don't litter, throw rubbish in the garbage bin.
4.The sun is very bright, lets sit under the shade of the tree.
5.I like gathering stamps.
6.My cousin had a fever yesterday.

Cheers ^^