声音在传播过程中，下列说法正确的是（）

根据所给首字母或单词提示, 写出正确的单词完成短文。

    On Sunday morning, I usually get up late. It is about 8:20 a.m. A____ I eat my breakfast, I often go to a shopping centre w____ my mother. The shopping centre is near my home, s____ we walk there. The shopping centre has a good n____.It is called “新世纪购物中心” in Chinese. It doesn't have an English name. Can you help to put it into E____?It is new and big. There are many t____ there, such as TVs, fridges, bikes, food and drinks. And the things there are usually good and c____.There are many p____there. They are men and women, old and young. Parents must look after their c____. The workers there are nice and f____. If you come to my home, I can take you there and have a look.

设$x,y\in R$，向量$\overrightarrow{a}=\left(x,1\right),\overrightarrow{b}=\left(1,y\right),\overrightarrow{c}=\left(2,-4\right)$且$\overrightarrow{a}\perp \overrightarrow{c},\overrightarrow{b}\parallel \overrightarrow{c}$，则$\left|\overrightarrow{a}+\overrightarrow{b}\right|=$ (     )