标准物质的作用是什么？对它基本要求是什么？

(2013·四川宜宾五校第二次调查考试)Teachers’ Day is a time to be________to all teachers who deserve special recognition.

A．available　　

B．grateful

C．generous

D．ridiculous

A terrible earthquake happened in Wenchuan, _____drew the attention of the whole nation at once.

A．that

B．where

C．which

D．what

下面四个数哪个最大

A．0.3

B．2/5

C．1/3

D．0/1π

下颌运动的制约因素是（）

A.右侧颞下颌关节

B.左侧颞下颌关节

C.牙

D.神经肌肉结构

E.A+B+C+D