A: Hi, Mr. Smith. Tomorrow I'm going to a formal western dinner party for the first time. ____

B: Sure. First, when you sit down at the table, take your napkin, unfold it and put it on your lap.

A: What does dinner start with?

B: A small dish.

A: ____

B: You should keep the knife in your right hand and the fork in your left. Don't take more food than you need. It's polite to finish eating everything on your plate.

A:____

B: No. You should try to speak quietly and smile a lot.____

A: What should I do when I drink to someone's health?

B: You should raise your glass and take only a sip.____

A: Thanks a lot.

B: You're welcome.

    If you are a little afraid when you walk alone at night, you can phone your family to make sure they know you are s____ But making calls may make you the target (目标) for bad people.

    Now there is an app and i____lets your family know your journey. And it will call for help when it feels you're i____danger.

    The app is c____ Companion(同伴). Before you start your journey, you input your starting place and your finishing place. Then you s____ them to your companion. The companion can be anyone in your phone book, and they don't n____to have the app.

    The app will tell your companion w____you are at any time. And it will show a button(按钮) on your phone screen every few m____asking “Are you OK?” If you don't press the button in 15 seconds(秒), your companion will get an alarm(报警). And the app will be ready to call the police for h____.

With the app, you will never be w____about going home alone.

已知线性方程组的增广矩阵为$\left(\begin{array}{c}0\\ 0\\ 3\end{array}\begin{array}{ccc}2& 4& -1\\ 1& a& 4\\ 5& 7& 1\end{array}\right)$，若该线性方程组无解，则a=____ ．

一四____

青蛙、家燕、春蚕个体发育的起点都是（  ）