*Marble Hill used to be on Manhattan island, until they dug the ship channel and redirected the Harlem strait to the south of Marble Hill, thus cutting it off from Manhattan island, and ultimately reconnecting it to the mainland.
In short, use a real site or one referenced by Wikipedia that's bona fide. Heck, I think I'll go edit the article now to say the East River is a national seagull and piping plover sanctuary with all vehicle crossings to be removed by July. Democracy of knowledge, innit grand?
Take this quiz in another 80 years and Long Island City and Brooklyn will be lapping up the skyscraper department.
You're thinking about it this way:
Q: Where is New York City?
A: Long Island
which does make it seem like a wrong answer. But you're just thinking of it wrong. You should be thinking like this:
Q: Which city is on Long Island?
A: New York City
This way it's obviously right. There is no other city on Long Island aside from New York.