(b) Method is not defined properly.
Reason: Following are some rules for declaring an abstract method:
- Abstract methods do not specify a method body, but they only have a method signature.
- Abstract methods are always defined inside an abstract class.
In the above code, MyFirstClass is an abstract class. It contains an abstract method named num() that is not defined properly. According to the rules discussed above, an abstract method only has a method signature, not the method body.