Which of the following sentences has an error in capitalization?
a. central park is one of new york's features i would love to visit someday.
b. i already heard the news about jamie and alex: they are going to have a baby!
c. the cruise ship crossed the atlantic ocean during very calm seas.
d. he looked at me carefully and stated, "don't worry because i'm here."

The sentence that has an error in capitalization is letter B. I already heard the news about Jamie and Alex: they are going to have a baby!

Explanation:

In American English, different circumstances determine whether or not to capitalize the first word after a colon. If we are merely listing things and the first word after the colon is not a proper noun, there is no need to capitalize it. The same happens when we have a phrase or incomplete sentence that does not start with a proper noun.

However, when we do have a complete sentence after a colon, even if it does not start with a proper noun, its first word should be capitalized. That is precisely the reason why the sentence in letter B is incorrect. After the colon, we a have a sentence that has a subject, a verb, and an object - a sentence that expresses a complete thought. Thus, the correct capitalization would be:

I already heard the news about Jamie and Alex: They are going to have a baby!

it b =a chorus ik for a fact