The correct answer is it lacked a bill of rights for the people.
This fight for a bill of rights for the people was lead by a group known as the Anti-federalists. The Anti-federalists feared that the new constitution did not guarantee a certain set of rights to citizens. This groups fear was that without this list of rights, the central (aka federal) government may become tyrannical and take away rights from citizens. This fear was rooted in America's experience as colonists under the control of Great Britain.
This is why the US Constitution ended up with a bill of rights, as Anti-federalists refused to agree to it until one was implemented.
