フリー問題

問題文

Two families of accessors remove the item at the front of a double ended queue. How does the family named after a poll behave once the queue has run dry?

選択肢

1. That family hands back an exception naming its emptiness as the outcome of that call.
2. That family hands back a copy of an earlier entry as the outcome of that call.
3. That family hands back a null reference for its caller to test as the outcome of that call.
4. That family hands back a stand in figure of zero as the outcome of that call.