I think that studying in pairs or groups is necessary____you want to learn from each other in class.

Do you have any pocket money ________—Sorry, I spent all my pocket money on my books yesterday.

October 24, 1860, the Qing government and the Britain sighed “the treaty ofBeijing”, ___ put an end to the second Opium war

Unless _____ to speak, you should remain silent at the conference [ ]

How happy we _______, if you had come with us to the party.