We can relax ourselves by taking part in school activities after long hours’ study; _______, we

can learn a great deal from other students.

A．therefore

B．but

C．however

D．besides

价值工程开展的最佳阶段是（）。

A．设计阶段

B．招投标阶段

C．施工阶段

D．投产使用阶段