问题
单项选择题
X射线的穿透性与被穿透物质相关的是()。
A.质量和厚度
B.密度和厚度
C.质量与组成
D.密度和组成
E.原子序数
答案
参考答案:B
X射线的穿透性与被穿透物质相关的是()。
A.质量和厚度
B.密度和厚度
C.质量与组成
D.密度和组成
E.原子序数
参考答案:B
There are many things that you should be careful with when you are alone at home. Read the following situations 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 you don't know how to use them, ask your parent. 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. "
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