We were busy ________ (get) things ready for the trial production when he phoned us.

Only when you have obtained sufficient data ________ come to a sound conclusion.

Senior members of the staff competed eagerly ________ the position of sales manager in the company.

新中国初期建立社会主义国营经济的主要途径是 _________。

规定取消公行制度，外商可与华商直接交易的条约是 ()