There is ______ thing as a free lunch. There may be a hidden cost.

—Must I turn off the gas after cooking ? --Of course . You can never be ___ careful with that.

I hate interruptions, _____when I ’m concentrating on my study.

They are _______ little children that you can’t blame them ______ much．

—“Could we put off the meeting?” she asked. —“ ____ ,” he answered politely. “This is the only day everyone is available.”