a series of book指一个整体,即一系列书,用单数形式谓语.
a stack of letters同理,一堆信,也是一个整体,用单数形式谓语.
the letters absolutely should be replied (to)我倾向于加to
a series of book指一个整体,即一系列书,用单数形式谓语.
a stack of letters同理,一堆信,也是一个整体,用单数形式谓语.
the letters absolutely should be replied (to)我倾向于加to