题目

构成中枢神经系统的是（   ） A．脑和脊髓                  B．脑和脑神经    C．脊髓和脊神经              D．脑神经和脊神经 答案：A15、A pilot asked all the passengers on board to remain ______ as the plane was making a landing． A．to be seating           B．seating         C．seated               D．seat