Answer 1

"pre" preserves the text as it is, regardless of spaces and if the text fits in the page (it will create a scroll bar)

"pre-line" leaves only a single white space if more than one have been written and sends the text to a new line if it doesn't fit in the page.

"pre-wrap" preserves the text but sends it to a new line if it is too long (instead of using the scroll bar).

Try it out by yourself by writing a long paragraph in the same row with many whitespace and you'll get what it is all about.