设l，m，n表示三条直线，α，β，γ表示三个平面，给出下列四个命题：
①若l⊥α，m⊥α，则l∥m；
②若m⊂ β，n是l在β内的射影，m⊥l，则m⊥n；
③若m⊂α，m∥n，则n∥α；
④若α⊥γ，β⊥γ，则α∥β.
其中真命题为

阅读下列材料:

材料一 古印度是世界四大文明古国之一。随着欧洲资本主义的迅速发展,西方人的航海殖民活动活跃,印度的厄运开始了。从1600年英国在印度建立东印度公司以来,印度被英国殖民统治长达三个多世纪。第二次世界大战后,英国在世界民族解放运动的浪潮推动之下,被迫宣布印度独立。

材料二 印度和巴基斯坦两国本是同根生。在十几个世纪中,生活在南亚次大陆的印度教徒与穆斯林共同创造了灿烂的文化。近半个多世纪以来,两国不断交恶的原因,归根到底是“分而治之”的殖民政策造成的克什米尔问题。

材料三 1947年6月3日,英国最后一任印度总督蒙巴顿公布印巴分治的“蒙巴顿方案”,根据“蒙巴顿方案”的规定,印度教徒占多数的地区划归印度,穆斯林占多数的地区归属巴基斯坦,克什米尔的归属问题却未能得到解决。

材料四 “蒙巴顿方案”的核心是按宗教,而不是按语言、文化或民族的区别来划分自治领。由此产生的印巴分立造成了无穷的后患。方案规定,各土邦可以自行决定加入任何一个自治领,这使查漠和克什米尔的归属问题成为悬案,造成印巴两国独立后立即围绕克什米尔问题兵戎相见。按照蒙巴顿分治方案,巴基斯坦由东、西两部分组成,分别称为东巴和西巴。东、西巴被印度隔开,相距约2 000千米。东巴人绝大部分属孟加拉族,使用孟加拉语;西巴人分属信德、旁遮普、俾路支和巴丹等几个民族。两地居民的文化和民族都不尽相同。东、西巴合为一体的基础仅仅是伊斯兰教。这种地理上的相互隔绝,民族、文化和语言的巨大差异,极易为内部分裂和外来干涉势力所利用。

请回答:

社会连线：“风声雨声读书声声声入耳，家事国事天下事事事关心。”请看下列材料：

材料一：走路、开车、吃饭、公交车上……无论何时何地，只要有空闲时间，他们总是拿着手机看，随着智能手机的普及，微博、微信、QQ等手机应用越来越丰富，越来越多的人喜欢在任何场合、任何时间玩手机，然而，随着手机“低头族”越来越多，因为路上玩手机、开车玩手机而造成车祸的现象频繁发生。

材料二：2015年10月5日，“诺贝尔生理学或医学奖”获奖名单揭晓，来自中国的女药学家屠呦呦获奖，以表彰她对疟疾治疗所作的贡献，屠呦呦女士也是首位获得诺贝尔科学类奖项的中国女科学家。在特殊历史时期，屠呦呦带领团队在极为艰苦的科研条件下，经过无数次试验，发现了青蒿素，开创了疟疾治疗新方法，全球数亿人因之受益。

阅读上述材料，结合自身感悟，运用所学知识，请你参与：

How to Study Smarter, Not Harder

    Here are some of our favorite study tips that will help any student study smarter, not harder:

Recite As You Study

    Reciting—saying things out loud should first take place as you read through each paragraph or section. Test yourself. This will help you to understand as well as learn faster because it is more active than reading or listening. It will also help you to notice your mistakes and the topics you have trouble understanding.

Take Fuller Notes

    Notes should be in your own words, brief and clear. They should be tidy and easy to read. Writing notes will help you better than just underlining as you read, since it forces you to rewrite ideas in your own words.

Study the Middle

    The best time to review is soon after you've learned something. You are more likely to remember the material at the beginning and the end of the lesson, so make sure you focus on the middle when you review.

Sleep On It

    Study before going to bed, unless you are very tired. It's easier to remember material you've just learned before sleeping than after an equal period of daytime activity, because your brain continues to think even after you've fallen asleep.

Combine Memory and Understanding

    There are two ways to remember: by memorizing and by understanding. Multiplication tables, telephone numbers, and math formulas are better learned by rote. Ideas are best learned by understanding.

    The more ways you have to think about an idea, the more meaning it will have; the more meaningful the learning, the better you can remember it. Pay attention to similarities in ideas and concepts, and then try to understand how they fit in with things you already know. Never be satisfied with anything less than a completely clear understanding of what you are reading. If you are not able to follow the thought, go back to the place where you first got confused and try again.