(x+1)⁴的展开式中x²的系数为

Complete the following passage with the words or phrases in the box. Each can be used only once.(将下列单词或词组填入空格，每空格限填一词，每词只能填一次)

 Today I'm going to talk about rainforests. Are you  ____    with them? They're interesting and exciting places! Many kinds of the world's plants and animals live in the rainforests.

 However, rainforests are____ now---they are disappearing very fast because they are cut down or burnt every day. As a result,   ____  animals and plants are dying out.

 Maybe you have never been to a rainforest, so why should you protect them  ____  ?  Rainforests are important to everyone. They are important because the plants in the rainforests make oxygen . We need oxygen to breathe.

足球运动员用头将足球顶向球门，这时施力物体是____；同时，头部会感到疼，此时施力物体是____；这说明力的作用是____。

1小时的 $\frac{5}{6}$ 是50分钟.