Correcting grammar (#20810)

add "event" to "De-couple an observer from an observable (event)."
remove redundant "program" in "Describes the program skeleton of a program."

guide/english/algorithms/algorithm-design-patterns/behavioral-patterns/index.md

@@ -16,14 +16,14 @@ Examples of this type of design pattern include:
 6. **Memento pattern**: Provides the ability to restore an object to its previous state (rollback).
 7. **Null Object pattern**: Designed to act as a default value of an object.
 8. **Observer pattern**: a.k.a. P**ublish/Subscribe** or **Event Listener**. Objects register to observe an event that may be raised by another object.
-9. **Weak reference pattern**: De-couple an observer from an observable.
+9. **Weak reference pattern**: De-couple an observer from an observable event.
 10. **Protocol stack**: Communications are handled by multiple layers, which form an encapsulation hierarchy.
 11. **Scheduled-task pattern**: A task is scheduled to be performed at a particular interval or clock time (used in real-time computing).
 12. **Single-serving visitor pattern**: Optimize the implementation of a visitor that is allocated, used only once, and then deleted.
 13. **Specification pattern**: Recombinable business logic in a boolean fashion.
 14. **State pattern**: A clean way for an object to partially change its type at runtime.
 15. **Strategy pattern**: Algorithms can be selected on the fly.
-16. **Template method pattern**: Describes the program skeleton of a program.
+16. **Template method pattern**: Describes the skeleton of a program.
 17. **Visitor pattern**: A way to separate an algorithm from an object.
 
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