OnTriggerEnter not work

i put 2 gameobjects(A and B) in my scenes and set the component box collider.
then i make A move forward B with script,and add the following script to B:

Code (csharp):

1.  
2. function OnTriggerEnter (col : Collider)
3. {
4. print("sth in!");
5. }
6. function OnTriggerExit (col : Collider)
7. {
8. print("sth out!"); 
9. }
10. function Reset ()
11. {
12. collider.isTrigger = true;
13. }
14. @script RequireComponent(BoxCollider)
15.  

and i hope when the A entered B, CMD show:"sth in".
but when my A entered.nothing happened.

ps:
1. i already add the box collider to A and B and set the B's Trigger checked!
2. when my First Person entered B.CMD show "sth in!"correctly!

why?!

 

Any trigger that moves needs to have a RigidBody also to work correctly. Set the RigidBody to Is kinematic and uncheck use gravity.

 

very thank you!