"This" implies the speaker thinks of the object as proximate in time or space, "that" implies he thinks of it as distant in time or space.
If you point to something on the the table right in front of you, you say, "What is this?" If you point to something across the room, you say, "What is that?"
"Why is this happening?" means something happening in the present. "Why did that a happen?" or "Why will that happen" mean something happened in the past and will happen in the future, respectively.
The grammar rules of @Jon Purdy relate space and time. If you write, "This is an example," the object of the "this" is taken to be immediate and right now. "If you write "that was an example," the object is taken to be not immediate and in the past (either literally if spoken or in the previous text if read.)
In your example
If you put the sentence before the list use "these"
Which one of these solutions do you prefer?
- Solution 1
- Solution 2
If you put the sentence after the list use "those."
- Solution 1
- Solution 2
Which one of those solutions do you prefer?
It's hard to see the subtlety but it becomes clear if the separation between the element and it's object is longer.
- Solution 1
- Solution 2
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Paragraph
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Paragraph
Which of these solutions do you prefer?
The reader will look in the text after and immediately before before jumping to the top.
- Solution 1
- Solution 2
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Paragraph
Paragraph
Paragraph
Which one of those solutions do you prefer?
The reader knows the refered to solutution are above/before and if the solutions at the top remain the only one's mentioned, will move his attention to these solution...see what I did there? When you read, "move his attention to these solutions" were did your attention go?
A helpful typo, I meant to write "move his attention to those solutions," which puts your attention on the proper object.