Explanation:

- Option 1: Change in demand – This occurs when customers’ preferences shift, causing products to become less popular. This situation causes obsolescence, but the change is generally gradual and expected, rather than sudden and unexpected.

- Option 2: Natural calamities – Events like earthquakes, floods, or fires can quickly make assets unusable, leading to their sudden and unexpected obsolescence.

- Option 3: Change in technology – New and advanced technology can suddenly make existing equipment or products outdated, even if they are still functional. This results in unexpected obsolescence known as technological obsolescence.

- Option 4: None of these – This means none of the above causes relate.

Correct Answer: Option 3 - Change in technology

Unexpected obsolescence usually happens due to rapid technological advances.