Explanation:

- Option 1: Natural calamities

These can cause sudden loss or damage of assets, but they don’t typically cause obsolescence. Obsolescence relates to assets or products becoming outdated or no longer useful, not to their physical destruction.

- Option 2: Change in demand

If consumers no longer want a product, it can quickly become obsolete. For example, typewriters became obsolete as computers became popular.

- Option 3: Change in technology

New technology can make older products or processes outdated and unusable, leading to unexpected obsolescence. For example, smartphones replacing traditional cameras.

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

Both a change in demand and a change in technology can unexpectedly cause obsolescence.