如图，四边形ABCD是等腰梯形，∠ABC=60°，若其四边满足长度的众数为5，平均数为 $\frac{25}{4}$ ，上、下底之比为1：2，则BD=____．

《望洞庭》是____代诗人____写的。这首诗写的是____季（节）的景色，诗中的“白银盘”是指____，“青螺”是指____。

福州江滨大道缤纷园入口处，安装了两盏“风光互补”景观节能灯，如图所示，它“头顶”小风扇，“肩扛”太阳能电池板。关于节能灯的设计解释合理的是 （   ）

   Many teenagers feel that the most important people in their lives are their friends．They believe that their family members don’t know them as well as their friends do．In large families，it is quite often for brothers and sisters to fight with each other and then they can only go to their friends for some ideas．
   It is very important for teenagers to have one good friend or a group of friends．Even when they are not with their friends，they usually spend a lot of time talking among themselves on the phone．This communication is very important in children’s growing up，because friends can discuss something．These things are difficult to tell their family members．
   However，parents often try to choose their children’s friends for them．Some parents may even stop their children from meeting their good friends．Have you ever thought of the following questions?
    Who chooses your friends?
   Do you choose your friends or your friends choose you?
   Have you got a good friend your parents don’t like?
   Your answers are welcome．

C₄H₁₀ $\underset{\Delta }{\overset{催化剂}{\to }}$ C₂H₆+C₂H₄，C₄H₁₀ $\underset{\Delta }{\overset{催化剂}{\to }}$ CH₄+C₃H₆．

如图是某化学兴趣小组进行丁烷裂解的实验流程．（注：CuO能将烃氧化成CO₂和H₂O，G后面装置与答题无关，省略）

按上图连好装置后，需进行的实验操作有：①给D、G装置加热； ②检查整套装置的气密性； ③排出装置中的空气等…