Assets are items that have value and can be owned or controlled. They are typically used to generate revenue or provide some benefit to the owner. In this question, all of the options listed could be considered assets for different reasons.

Explanation:
The correct answer is option 'D', all of the above, because:

a) A car:
- A car can be considered an asset because it has value and can be owned or controlled.
- It can be used for personal transportation or as part of a business (e.g. for deliveries or transportation services).
- It can also be sold or traded for money or other assets.

b) A mortgage:
- A mortgage can be considered an asset because it represents ownership of a property (e.g. a house or commercial building).
- The property can be rented out for income or sold for a profit.
- The mortgage itself can also be sold or traded as part of a financial investment.

c) A digital music file:
- A digital music file can be considered an asset because it has value and can be owned or controlled.
- It can be sold or licensed for use in media productions or performances.
- It can also be used as part of a marketing or branding strategy.

Conclusion:
In conclusion, all of the options listed are examples of assets for different reasons. They have value and can be owned or controlled, and can be used to generate revenue or provide some benefit to the owner.

Digital music file and car are assets so ans should be D also mortgage for a person are the assets submited to him by another person for taking some loan so mortgage also comes under asset