Option A is correct. wait() causes the current thread to wait until another thread invokes the 

notify() method or the notifyAll() method for this object.

Option B is wrong. notify() - wakes up a single thread that is waiting on this object's monitor.

Option C is wrong. notifyAll() - wakes up all threads that are waiting on this object's monitor.

Option D is wrong. Typically, releasing a lock means the thread holding the lock (in other words, 

the thread currently in the synchronized method) exits the synchronized method. At that point, 

the lock is free until some other thread enters a synchronized method on that object. Does 

entering/exiting synchronized code mean that the thread execution stops? Not necessarily

 because the thread can still run code that is not synchronized. I think the word directly in the 

question gives us a clue. Exiting synchronized code does not directly stop the execution of

 a thread.