必备品的反义词比如说我的办公桌上放着的一些物品是必备品,那些可有可无的物品该怎么表述呢?

The comb is personage love is necessary article,a lot of people in use after leaves some broken comb the hair,comb with these traditional cut hair in no way,after every use to spend a certain amount of time to do,so comb waste a lot of time,accumulate over a long period,the waste of time will be amazing,a let you don't have to spend and outside time can keep clean design Juhyun comb by creative product,the proposed Lee him self on the basis of traditional comb added a cushion,when use,put the cushion laid on the comb,produce and scalp rubbish will cut hair with the mattress-padded remove,and is forced out by the software,the pads comb,strong and durable rubber manufacturing,clean easily.

解题思路：下列物质中，能发生酯化反应的物质含有羟基或羧基，能发生加成反应的物质含有苯环或碳碳双键，能发生水解反应的物质含有酯基或肽键，能发生中和反应的物质含有羧基或酚羟基．

A、含有羧基能发生加成反应和酯化反应，六元杂环结构含有N原子具有苯环性质，能发生取代反应和加成反应，不能发生水解，故A错误；
B、含有羧基能发生中和反应与酯化反应，含有酯基能发生水解反应，含有苯环能发生加成反应，故B正确；
C、含有苯环、碳氧双键，能与氢气发生加成反应，苯环能发生取代反应，不能发生水解和中和反应，故C错误；
D、含有醇羟基能发生酯化反应，含有苯环能与氢气发生加成反应，含有肽键能发生水解反应，不能发生中和反应，故D错误．
故选B．

点评：
本题考点： 取代反应与加成反应；消去反应与水解反应．

考点点评： 本题考查了物质性质的确定，难度不大，根据物质中含有的官能团分析判断即可，官能团决定其性质．

First,I would bring a water treatment device because I need to purify the water nearby in order to survive.Second,I would bring a knife to guide myself from animal's attack.Then,food seeds are needed because I could plant them and get the necessary food from it.What's more,the seeds could be collected after they come to flower.Last,I would bring a camera because I want to take pictures for memories.

my ideal travel was hiking.Taking a pack and some necesaries,several people just go hiking.Since I think hiking is the best way to approach nature.Walking and appreciating the beaty of nature is a fan...

This year I 'm going with my parents went to Hainan tourism, we need to bring the following things:
1, hainan tourism should be the necessary items slippers, sunglasses, sun umbrella, sunscreen, etc.
2, free activities to the hotel reception hosting their best of documents and valuable goods, travel for hotel card.
3 and the carsick, seasick, take appropriate before drink a glass of cold water, take don't eat sweets when.
4, with otitis media, cardiovascular, heart disease, asthma group members can't participate in diving, avoid by all means is secretly sea swimming.
5, sanya seafood for sea water pollution less, and the people are good at cooking, the seafood taste beauty, however, seafood is good, but not excessive.
6, traveling, please prepare good personal commonly used drugs (such as a band-aid, expectorant, cold medicines, carsick medicine, etc.), for a rainy day.

One can feel at ease when him use it.In addition,to a normal man,the shaver is an important requisite.If without it,thus will has effect on men's self-esteem.
希望能帮上你!

作B′M′∥C′D′,C′M′⊥B′M′于点M′．
粉笔的半径是6mm．则边长是6mm．
∵∠M′B′C′=60°
∴B′M′=B′C′•cos60°=6× 12=3．
边心距C′M′=6sin60°=3 3mm．
则图（2）中,AB=CD=11×3 3=33 3mm．
AD=BC=5×6+5×12+3=93mm．
则周长是：2×33 3+2×93=66 3+186≈300mm．
故答案是：300mm．

根据题意,
矩形的对角线是10支粉笔的直径 10*12=120mm ,宽度是5支半粉笔的直径 5.5*12=66 mm
根据勾股定理 长度为 √(120²-66²)=100.22 mm
矩形周长 = 2 *（100.22+66）= 332.44 mm
--------------完善下----------------
矩形的对角线是9支粉笔的直径 + 一支粉笔的外接正方形的对角线长
9*12 + √(2*12²) = 108+17=125 mm ,
宽度是5支半粉笔的直径 5.5*12=66 mm
根据勾股定理 长度为 √(125²- 66²)=106.2 mm
矩形周长 = 2 *（106.2+66）= 344.4 mm