<em /><u><em>"She did not understand what happened."
</em></u>It is a complete sentence since it has a subject (she) and a verb (understand), and is independent (i.e. doesn't require another clause to make sense<u><em>
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Red is the adjective because it describes the color of the truck.
If you really like him, than date him.If you can find someone else you like better than don't date with him.
Like...
My Mom can trace our ancestors back 100 years.
D