美术课可以分成（）、（）、（）。

不等边三角形ABC的两条高的长度分别为4和12，若第三条高的长度也是整数，那么这条高的长度等于______．

儿童进餐时间不应少于（）分钟，保证儿童吃饱每餐饭。

Below is an entry taken from an English dictionary．

小题1:“Be careful not to scratch the furniture" most probably means “Be careful not to          ”．

A．remove any marks

B．damage its surface

C．make any noises

D．change its position小题2:The word "scratch" in "Some drawings had been scratched on the back of the door" has the same meaning as in“      ”．

A．We scratched some of the dirt away

B．The car's paintwork is badly scratched

C．The dog; kept scratching at the door to go out．

D．They scratched lines in the dirt to make marks小题3:“She．had scratched because of a knee injury" might imply that “She couldn't       ．

A．take part in a race

B．cancel a prepared activity'

C．make a living af6ne

D．make enough money小题4:When the French girl says "I learned German from scratch iii six months she means she       ．

A．had previously well prepared

B．was unsatisfied with her German

C．knew no German before that

D．found few materials available

经检测，某食品每百克中视黄醇当量为310ug，能量577kJ。先已知推荐每日膳食中营养素供给量，成年轻体力劳动者视黄醇当量为800ug，能量为2600kcal。营养素密度为( )

A．0.2219

B．0.5373

C．0.3875

D．2.5806

请简述进入六氟化硫电气设备低位区域或电缆沟进行作业时，对于含氧量和六氟化硫其他含量的要求？