I went there two days ago. Everything seemed to be fine, but
(1) two days later, things changed dramatically.
(2) two days after, things changed dramatically.
(3) things changed dramatically after two days.
(4) things changed dramatically two days later.

I'm confused with the order of the "time adverb" in a sentence.

Are they interchangeable?
before two days/ two days before
after two days/ two days after/ two days later
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Comments  (Page 3) 
I really don't know...that's a good questions. I'm sure there's some kind of secret part-of-speech that I don't know about, and those words fall into that category in this situation. heheh
You might find this following [url="http://www.getitwriteonline.com/archive/022703.htm"]link[/url] helpful on prepositions at the end of a sentence.

I especially like Churchill's quote....
This is the kind of impertinence up with which I shall not put.

I have seen numerous variations of Churchill's quote, so many that I am not sure which quote is the actual true quote. Here's another...
This is something up with which I will not put.
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looked it up with gurunet...

from the article on in:

To or toward the inside: opened the door and stepped in.
To or toward a destination or goal: The mob closed in.
Sports. So as to score, as by crossing home plate in baseball: singled the runner in.

from the article on on:

In or into a position or condition of being supported by or in contact with something: Put the coffee on.
In or into a position of being attached to or covering something: Put your clothes on.
In the direction of something: He looked on while the ship docked.

Toward or at a point lying ahead in space or time; forward: The play moved on to the next city.
At or to a more distant point in time or space: I'll do it later on.

So it could be an adverb.
looked it up with gurunet...

GuruNet is great, isn't it?
Students: We have free audio pronunciation exercises.
Sometimes days begin with nothing to look forward to.

How about this one? 'to' is a preposition at the end of the sentence. How can I rewrite it?
Wild guess...

Sometimes days begin to which nothing to look forward.

You can end sentences with prepositions. (See Churchill's quotes above.) So I wouldn't worry about it.

Sometimes days begin with nothing to which you can look forward.
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Thanks there.