請幫我改這幾句英文

1.我於5月20日,已收到本書.
I received the book on May 20.
I have received the book on May 20.
(The second sentence is used when it relates to the present. For instance, "I have received the book on May 20 so that I can read it now.)

2.我在夏天將會被派往澳洲,我比較喜歡住在效區.
I will be sent to Australia in summer, I prefer to live in countryside to city.

3.我和我同房將會搬去新單位,這兒有兩間房,我同房住大房,她是一個好同房,當她早回到家時,她會煮晚飯給我,而我會洗碗.
I will move (to)the new department with my roommate(.) (There) (are) two bedrooms(.) (My) roommate lives in the bigger room(.) (She) is a good roommate(.) (She) always cooks the dinner for me when she (goes) home early(.) I (wash) the (dishes) after dinner(.)

4. 當我們到達火車站時,火車已經開動了。(第二句是正確的,但第一句可以嗎?)
The train (had) moved when we arrived at the railroad station. (The action "the train moved" is earlier than the actoin "we arrived at the railroad station" so we use the past perfect tense for the earlier action.)

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Suggested sentences:
1. I received the book on May 20.
2. I will be sent to Australia in summer. I prefer living in the countryside to living in downtown.
3. My roommate and I will move to a new department. There are two bedrooms, and my roommate will live in the bigger one. My roommate is a nice person. She always cooks dinner for me when she returns home early. I will do the dishes after dinner.
4. The train started moving when we arrived at the railway station.

2010-06-04 21:24:24 補充：
The first words of the sentences seem to be hidden??!!
1. I received...

2. I will be sent .....
3. My roommate .....
4. The train started ......

1. usually "I received the book on May 20" is ok to convey the Chinese meaning, but if the sense of "already" needs to be emphasized, then the 2nd sentence is preferred
2. the 1st part of the sentence is correct, but for the 2nd part, usually we say "prefer this to that", so your "than to' is repeated. you can say "prefer living in the countryside to downtown (=city)"
3. you can change it to:
My rommate and I will move to a new apartment (apartment=flat, department=部門), where there are two bedrooms. My roommate will live in the bigger room. She is nice, as she always cooks dinner for me when I return home early. I help her to do the dishes afterwards.
we usually say "there is/are A in B" to express "B contains A/A is in B"
do the dishes=wash the dishes
4. if you SEE the train leaving once you arrive, you need to use the 2nd sentence (continuous). if you know (hear from other people) that the train has already departed after your arrival (you didn't see it moving), you can use the 1st sentence, but correct it to:
The train had departed when we arrived at the railroad station.
past perfect: used to describe actions happened BEFORE those in past tense

0.0 all correct wo~