放射性：
参考答案：
在核衰变过程中总是放射出具有一定动能的带电或不带电的粒子，即α、β、γ射线，这种现象称为放射性。
一般而言，达到面积守恒和重量守恒在（）岁。
A.6～8
B.7～9
C.8、9～10
D.11～12
How many time do you spend with your parents? 1.___________
Your parents are your dearer people in the world 2.___________
when you are young. And they always care of you 3.___________
deep. But even though many children still love their 4.___________
mum and dad, families may become more close 5.___________
as you get older. The end of the year is a time for 6.___________
families to get together. Have you ever thought of 7.___________
how you can show your parents that you love them? 8.___________
Find a chance and do something for them or to have 9.___________
sincere talk with them. If you can do this, your parents 10.___________
will be very happy.
