[Grammar] Which is why / That is why..?

[wotcha22]

1. Which is why they drive Fords in Ohio.

2. That is why they drive Fords in Ohio.

3. Which is because I got up late.

4. That is because I got up late.


I came across the 1st sentence today, which I hadn't seen before, and wonder 1 and 3 are same as 2 and 4 in meaning.

 

[Tarheel]

The first is not a sentence but is a dependent clause looking for some words to hang with so it can become part of a sentence. Number three is similar. Numbers two and four are fine as sentences, but we are missing some critical information. (Why do they drive Fords in Ohio?) I can imagine number four being something like:

I was late for work today. That is because I got up late.


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