Which of the Following Is a Characteristic of the Core

Which of the following is a characteristic of the core?

A) The core is the set of all allocations that cannot be blocked.
B) The core is the set of all allocations where the value realized by the members of the coalition are same as what they can realize individually form the core.
C) Cores are broken when one or more participants withdraw from the coalition.
D) Any allocation that makes even one of the parties to the transaction better off is in the core.