阅读下面短文，根据上下文填入适当的词语，或使用括号中的词语的适当形式填空，并将答案填写在非选择题答题卷上标号为16—25的相应位置。
An earthquake can often cause damage. Knowing how to prepare for such 16 event can directly affect your chance of survival.
If you are outdoors, find an open area free 17 trees and tall buildings. If you 18 (drive) when an earthquake hits, slow down and stop in a clear place. Remember that you have to stay in your car. Do not park near buildings 19 under bridges. If you are indoors, you must protect yourself from 20 (fall) objects by finding a safe place in your home. For example, you can hide under something. This most often means a heavy table or desk 21 is large enough. It is important for you to know where the furniture is 22 an earthquake. Besides, make sure that all the family members knows the best place to hide 23 in each area of the house.
For families with young children, it’s recognized to be more important to practice 24 to do in the earthquake. Make sure your family has a plan of action, and tell your children where to meet each other. 25 is also wise to be prepared by taking a First Aid class to learn something useful for a possible disaster.
。则X表示________粒子（用符号表示）；若已知
的质量为m1，
的质量为m2，
的质量为m3，X的质量为m4，则这个反应释放的核能为___________。