单项选择题
A．A whole night. B．Twenty-four hours. C．A whole week. D．Three days.
A．how to start a university B．the world-famous colleges in America C．how colleges have changed D．what kind of lesson each college teaches
A．to describe how pruning a tree is done B．to discuss different ways of pruning trees C．to give practical instructions for pruning a tree D．to explain how a tree wound gets diseased and heals