Explanation:

Let’s break it down:

- Option 1: Natural calamities

- These are things like earthquakes, floods, fires. They can destroy assets suddenly, but that’s not obsolescence—that’s just loss or damage.

- Option 2: Change in demand

- This is when customers no longer want a product, making the stock or equipment you have less useful or outdated.

- Option 3: Change in technology

- New inventions or upgrades can make old tools or products useless, even if they’re in perfect condition.

- Option 4: Both (b) and (c)

- The real culprits behind unexpected obsolescence are changes in demand and technology. They can suddenly make things worthless, often without warning.

So, the right answer is Option 4—Both (b) and (c). Natural disasters wreck things, but obsolescence is all about usefulness fading away thanks to market or tech shifts.