概述中枢神经系统的分布。
参考答案：
中枢神经系统包括脑和脊髓。脑可分为端脑、间脑、中脑、脑桥、小脑和延髓。通常把中脑、脑桥和延髓合称为脑干。
规律的客观性是指
A．它的存在和发生作用是无条件的
B．它可以被人的感官感知
C．它的存在和发生作用不以人的意志为转移
D．人们不能掌握它，只能服从它
Ten years ago the population of our village was ________that of theirs.
A．as twice large as
B．twice as large as
C．twice as much as
D．as twice much as
