按“先进先出”原则组织数据的数据结构是 【3】 。

There are many things that you should be careful with when you are alone at home. Read the following solutions to protect yourself.
Keep the door locked when you are alone at home. Many people think it’s the best way to protect themselves.
Keep a list of phone numbers to call for help-such as 110, the police station or a neighbor’s number.
Be careful with the electrical appliances（电器）. If don’t know how to use them, ask your parents. Make a safety check before going to sleep.
Look through the keyhole when you hear the doorbell. If there are strangers, ask “Who’s that?” with the door locked and say “Come back later.” Don’t tell them that your parents are away. Say “Mum’s having a shower.” or “Dad’s having a sleep.”

Protect Yourself When Home Alone
Situations	Solutions
You are alone at home	Keep the door   71
To   72	Keep a list of phone numbers
Before   73	Make a safety check of the electrical appliances
Talk to the strangers	Ask “   74    ?” with the door locked.
	Don’t say your parents   75