阅读短文，从方框中选择恰当的词并用其适当形式填空，使短文完整、通顺。每词限用一次，其中有两个词是多余的。

as，sound，they；clever，send，imagine，heavy，hear，lucky ，know，if，follow

    Mr. and Mrs. Brown were farmers in South Australia．They lived there for many years．They had a kangaroo(袋鼠)in____family．The kangaroo was called Lulu．Several years ago，Mr. Brown’s son gave Lulu to him ____a gift for his 60th birthday. Soon Mr. Brown and Lulu became good friends and Lulu often ____ him around the farm．
    One day when Mr. Brown was working on his farm，a(n)____tree branch(树枝)fell on top of top of him suddenly(突然)．Mr. Brown fell to the ground(地面)and didn't____what happened next．Lulu stood next to Mr. Brow’s body．She started barking(叫)and didn't leave Mr. Brown．“She ____like a dog．She barked and barked．And she didn't stop．”said Mrs. Brown．After ____Lulu's barks, Mrs. Brown quickly went to see what had happened．She saw Mr. Brown lying on the ground and____him to the hospital right away．____，Mr. Brown was saved．
     “Lulu is great!”said Mr. Brown．“She saved me! She is a friendly and very ____ kangaroo．”After Mr. Brown left the hospital, he took Lulu everywhere he went．

已知向量 $a,b$ 满足 $\left|a\right|=1,\left|b\right|=2,$   $a,b$ 的夹角为 ${60}^0$ ，则 $\left|a-b\right|$ =____.

填入下面句中横线处的语句，与上下文衔接最合适的一组是（   ）
不只一位先贤指出，一个人无论看到怎样的美景奇观，如果没有机会向他人讲述，他绝不会感到快乐。一个人无论遭遇怎样的不幸，如果有向心爱的人倾诉的机会，他的痛苦自然会减轻。________，________。没有任何人倾听，绝对的孤独，快乐会成为失望，痛苦会成为绝望！

点P₁（$x_1$，$y_1$），点P₂（$x_2$，$y_2$）是一次函数$y$＝－4$x$ + 3 图象上的两个点，且$x_1$＜$x_2$，则₁与₂的大小关系是（    ）

已知等差数列$\left\{a_n\right\}$满足$a_2+a_4=4$，$a_5=4a_3$，则数列$\left\{a_n\right\}$的前10项的和等于（   ）