用数学归纳法证明“（n+1）（n+2）…（n+n）=2ⁿ•1•2•…•（2n﹣1）”（n∈N₊）时，从“n=k到n=k+1”时，左边应增添的式子是____ 

读课文《太空生活趣事多》排序

____人稍一使劲就会飘到半空中

____在宇宙飞船里走路更有趣。

____咳嗽一声就有可能后退好几步

____宇航员都穿鞋底带钩的鞋子

____为了能平稳地走路

____好牢牢地钩住带网格的地板

马克思指出，人类社会的发展是一个自然历史过程。即人类社会的发展同自然界的发展是一致的，是客观的，是不以人的意志为转移的、合乎规律的辩证发展过程。对此理解正确的是（  ）

①人类社会和自然界的发展是完全一样的

②人类社会和自然界一样具有物质性

③人类社会和自然界一样，一切活动无需人的意识的参与

④人类社会的发展和自然界一样，是一个客观物质过程

    I like listening to music in my flee time. My favorite song is Another World by One Direction. I also like reading books and one of my favorite books is The Old Man and the Sea. But I like making clothes best. I think it is very interesting.

                                                                  Emma

    In my free time, I like reading books, drawing and playing volleyball. I also enjoy talking with my friends and playing the piano. I have piano lessons every Thursday and Sunday.

                                                                        Bill

    In my free time, I often help my parents do the housework. I clean the rooms, wash the dishes, walk the dog and help my sister with her studies. But my favorite thing is cooking. I want to be a great cook in the future (未来).

                                                                    Tina

    I like doing volunteer (志愿者) work inky free time. I go to the old people s home with my classmates twice a month. And sometimes I go to the market to help old people. I also help clean the park in my neighborhood.

                                                                       Jessica