During the day we work and play; at night we sleep. Our bodies rest while we sleep. In the morning we are ready to work and play again. While we are asleep our bodies grow most. Children usually need more sleep. We can get our lessons better and we feel better too, when we have plenty of rest. Boys and girls need ten hours of sleep every night when they are eight or nine years old. Our bodies need lots of air when we sleep. If we do not get enough fresh（新鲜的）air we’ll feel tired when we wake up. While in bed we must not cover our heads. If we do, our lungs（肺）will not get enough fresh air. If we open our windows at night we can have plenty of fresh air. Cool air is better then warm air. Boys and girls must get enough sleep if they want to grow and be strong.

小题1: Our bodies grow most while we are___________.

A．eating

B．playing

C．sleeping

D．waking小题2: Which is the best air for us?

A．fresh air

B．Cool air

C．Warm air

D．Dry air小题3: Too little sleep makes us_________.

A．nappy

B．hungry

C．tired

D．grow小题4:How much sleep should boys and girls of nine years old have every night?

A．Eight hours

B．Nine hours

C．Ten hours

D．Seven hours小题5:What do the lungs need most?

A．Fresh air

B．Food

C．Rest

D．Exercise

从100gt℃时KNO₃溶液中恒温蒸发掉10g水，析出2g晶体，再恒温蒸发掉10g水，又析出5g晶体，t℃时原100g溶液是______（填“饱和”或“不饱和”）溶液，t℃时KNO₃饱和溶液中溶质的质量分数为______．