①若a＜b，则a²＜b²；

②若a≥b＞﹣1，则 $\frac{a}{1+a}$ ≥ $\frac{b}{1+b}$ ；

③若正整数m和n满足m＜n，则 $\sqrt{m\left(n-m\right)}$ ≤ $\frac{n}{2}$ ；

④若x＞0，且x≠1，则lnx+ $\frac{1}{1nx}$ ≥2．

其中所有真命题的序号是____

苹果的单价为a元/千克，香蕉的单价为b元/千克，买2千克苹果和3千克香蕉共需（　　）

    Have you been asked for money by some disabled beggars (乞丐) while you're enjoying shopping? Do you have any pity on them who are so poor and lonely or do you just feel afraid of their terrible shapes? As one of the most special groups, disabled people's living conditions — not only their material (物质的) conditions, but their mental (精神的) world — really need improvement.

    The treatment for disabled people should go like this: First, don't look down upon them. Don't be afraid of looking at the terrible shapes of the disabled. Try to treat them equally. Because they are a part of the society (社会),we cant discard (抛弃) them. The second is to help them as much as we could. If you can be a volunteer and do some work for the disabled people, that would be very nice. That does help not only to the disabled people but also to yourself because you will feel good after your kind action.

    If every one of us gives a little love, the world will become a beautiful wonderland!

近来，频发的校园暴力事件引起了社会的广泛关注。

材料一：某校初二学生王某因怀疑同桌向老师打小报告，心生怨恨，一气之下对同桌拳打脚踢，最终被学校发现并严肃处理。

材料二：日前，国务院教育督导委员会办公室向各地印发《关于开展校园欺凌专项治理的通知》，要求各地各中小学校针对发生在学生之间，蓄意或恶意通过肢体、语言及网络等手段，实施欺负、侮辱造成伤害的校园欺凌进行专项治理。