Answer:
The statement which has an error in capitalization is C. I already heard the news about Jamie and Alex: they are going to have a baby!
This is because we can capitalize a statement after a colon if it is an independent statement. Hence, the letter 't' in the word 'they' need to be capitalized after the colon.
The correct statement would hence be written as:
I already heard the news about Jamie and Alex: They are going to have a baby!