Exactly______ the potato was introduced into Europe is uncertain, but it was probably around 1565.
. When she woke up, she realized that things she had dreamed about could not _______ have happened.
Mr. John was always___the poor and the sick, often providing them with free medical care.
--- Jim, do you have the time? --- _______. --- Never mind. Thanks anyway.
In his address at two-day APEC Economic Leaders Meeting, President Hu _______ the APEC to reform itself to raise the efficiency of cooperation so as to keep advancing _______changing times.
His proposal is _______ to all of us and you do not need to tell us more about it.