Explanation:

Here’s the thing—the question is about what triggers unexpected obsolescence.

- Option 1: Natural calamity

- Disasters might cause loss or destruction, but that’s not really “obsolescence.” The product is lost, not outdated.

- Option 2: Change in demand

- When people suddenly stop wanting a product, that product often becomes obsolete even if it’s still functional.

- Option 3: Change in technology

- New tech can make existing products useless almost overnight. Think of how smartphones made MP3 players obsolete.

- Option 4: Both B & C

- This sums up the last two points. Sudden shifts in demand and/or tech can both cause unexpected obsolescence.

So the correct answer is:

Option 4: both B & C