that的運用??

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I don`t know that mary is coming.(我不知道瑪莉要來)

THERE ARE MISTAKES IN YOUR SENTENCE!!!
1) don't <--------------
2) Mary <----- a name You need to capitalize it.

You should change your sentence to
- I don't know if Mary is coming.
( I don't know whether Mary is coming or not.)
*** Mary has not come yet. You are just telling people that you have no clue if she is coming.***
- I didn't know if Mary was coming.
- I didn't know whether Mary was coming or not.

***Mary is probably on her way.******
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THAT
Examples:
-He said (that) he would come to my place.
"that"= optional
-I am afraid(that) he won't like my new car.
"that" = optional
A that-clause typically functions as a subject or a direct object (but can also function as an apposition in a noun phrase, as a predicative, or as a complement of an adjective).
In conclusion, "that" is often omitted in oral English, but in written/formal English,
we normally use it.


2009-07-15 11:38:01 補充：
I don't know that Mary is coming.

Your sentence is right.

"Mary is coming" is the direct object.

2009-07-15 11:40:12 補充：
Sometimes we construct broken sentences if we drop the word "that".


I don't know Mary is coming. <------Two broken sentences here!

Every coin has two sides. For written English, I suggest you use it.

2009-07-15 11:41:49 補充：
I don't know + Mary is coming *********

We call this kind of clause "that clause".
The "that clause" in this sentence tell us the "thing" I dont know.
We can omit the word "that" in this sentence. Many people would omit it.

e一句就可以吾+
旦系加左會好d甘姐.

that可代替what/which/who

e.g.

1)
Mary is a girl who is 5 years old.
亦等如
Mary is a girl that is 5 years old.