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.

最简单的电话装置是由　____ 　、　____ 　和　____ 　组成，它们应____ 　联在电路中，其中的主要元件是电磁铁．

①用调好的天平测量出空烧杯的质量为30g；

②取适量牛奶倒入烧杯，用天平测量出牛奶和烧杯的总质量，天平平衡时所用砝码和游码的位置如图甲所示；

③将牛奶全部倒入量筒中，读出牛奶的体积V，如图乙所示．