句子grammar問題

I went to Apple Supermarket to buy a tooth brush yesterday. When I arrived at
the supermarket, there were many people in the supermarket.
第2句應改成:
When I arrived at the supermarket, there were many people. 唔洗再加"in the supermarket"...

When I did homework, I was tired.
呢句應改成:
When I was doing homework, I was tired. 因為係做緊功課先累，唔會一做就累

I started to do my homework at 8:15pm last night. It was difficult for me to do my homework because my homework was difficult.
呢句應該就無錯Grammar

2013-02-14 18:20:07 補充：
"When Mary massaged my legs, I felt comfortable."

"When I lived in USA, I believed in God."

"When I was doing my homework, I smelt frangrance."

"When I was repairing the fan, Sam was singing songs."

"When Mary shouted, she was horrible."

呢幾句GRAMMAR無錯......
只係第3句嬲尾果個字串錯左~~
應該係fragrance

The dishes were tastly意思是啲碟子好好味道，雖然可能你曾經被教一道一道的餸菜叫做dishes，但這裏正確的寫法是the food is tasty或者列出每道dish名稱或你食了甚麼。

When I arrived at the supermarket, there were many people in there.(同一句出現相同的名詞時可用代名詞…這裏不用in there亦可以了)又因為上句已經講明你係去了Apple Supermarket，可以把句子改為There were many people when I arrived there.

When I did homework, I was tired.
這句有錯但改法則要看你想表達的意思，我就會(估你是想)講「當我做完了功課…覺得很累」
When I finished doing homework, I felt tired.

2013-02-14 12:00:29 補充：
… It was difficult for me …(中間這些是前面的名詞可以省去) because it was difficult.(用代名詞it)除了詞語重複grammar不算錯，但兩次difficult其實重複意思，所以單一句It was difficult for me.已經寫完。寫得多反而是錯。

最後補充的幾句的結構沒錯，但意思卻有問題。只有第四句是grammar和意思都對。

2013-02-14 12:00:41 補充：
例如:
"When I lived in USA, I believed in God."
意思即是「當我住在美國時我信神….當我不在美國時便不信神了」，如果你想說「當我(以前)住在美國時，我信了神…」便要寫成"I accepted God when I was living in USA."！