所谓光泽，就是彩色涂层钢板（）把投射其上的光线向一个方向反射出去的能力。A.冷压贴膜

We should well balance our work and relaxation, and only by doing that, as everybody would agree , ______ a good state of mind.

A．can we have

B．we can have

C．need we have

D．we need have

It ________ at the crossroads ________ he was killed in the accident the other day.

A．is; that

B．was; that

C．is; where

D．was; where

将305 g NaHCO₃和Na₂CO₃的混合物加热至质量不再减少为止，待冷却后，称得剩余固体质量为212 g。则原混合物中Na₂CO₃的质量分数是多少？

罗红霉素为常用的消炎药，用于治疗呼吸道感染、耳鼻喉感染等。根据罗红霉素的化

学式(C₄₁H₇₆N₂O₁₅)回答下列问题(友情提示：C₄₁H₇₆N₂O₁₅的相对分子质量为836)：

(1)罗红霉素由      种元素组成，其中氢元素与氮元索的质量比        ；

(2)罗红霉素中氢元素的质量分数             (计算结果精确到0 1％)。

胸段脊髓受损在脊髓休克过去之后，排尿功能障碍的表现为

A．交感兴奋导致尿失禁

B．尿频

C．尿急

D．尿多

E．副交感兴奋导致尿失禁