Option C is wrong. See the note above on Islands of Isolation (An object is eligible for garbage collection when no live thread can access it - even though there might be references to it).
Option B is wrong. "Never again be used" does not mean that there are no more references to the object.
Option A is wrong. Even though Java applications can run out of memory there another answer supplied that is more right.
Option B is correct. If an object can be accessed from a live thread, it can't be garbage collected.
Option A is wrong. Runtime.gc() asks the garbage collector to run, but the garbage collector never makes any guarantees about when it will run or what unreachable objects it will free from memory.
Option C is wrong. The garbage collector runs immediately the system is out of memory before an OutOfMemoryException is thrown by the JVM.
Option D is wrong. If this were the case then the garbage collector would actively hang onto objects until a program finishes - this goes against the purpose of the garbage collector.