How many types of inheritance can be used at a time in a single program?

In a single program, you can use as many types of inheritance as you need. The main types of inheritance are:

1. Single Inheritance: When a class extends another class.
2. Multiple Inheritance: When a class can inherit from more than one class. Note that multiple inheritance is not supported in some languages like Java.
3. Multilevel Inheritance: When a class extends a class which extends another class, and so on.
4. Hierarchical Inheritance: When one class serves as a superclass (base class) for more than one subclass.
5. Hybrid Inheritance: A mix of two or more types of inheritance.

The number of these types you can use in a single program depends on the specific requirements of your program and the language you are using. Some languages may not support all types of inheritance.