Which of the following is the correct sequence?

Concept: Storage-unit sizes follow a fixed hierarchy — KB < MB < GB < TB < PB, each unit roughly 1024 times the previous one. A chain such as "A > B > C > D" that mixes different units is a valid descending sequence only if every consecutive comparison in it is actually true, not just the first term.

Checking each option:

• 25 KB > 12 MB > 10 GB > 20 PB — fails immediately: a kilobyte is far smaller than a megabyte, so 25 KB is not greater than 12 MB. The chain rises from the smallest unit to the largest, the reverse of what a valid descending sequence needs.

• 20 TB > 10 GB > 12 MB > 25 KB — every step drops to a smaller unit (terabyte → gigabyte → megabyte → kilobyte), and each comparison holds numerically at that scale, so the whole chain stays consistent from start to end.

• 10 GB > 12 MB > 20 TB > 25 KB — the first two comparisons hold, but placing 20 TB after 12 MB is wrong: a terabyte is a far larger unit than a megabyte, so this step breaks the chain partway through.

• 10 PB > 10 GB > 10 TB > 10 MB — opens correctly with the largest unit, but 10 GB is placed ahead of 10 TB; at the same numeric coefficient a terabyte is larger than a gigabyte, so this step reverses the true relationship and breaks the chain.

Cross-check: Only the chain that keeps every adjacent comparison true throughout — following the full hierarchy TB > GB > MB > KB without any reversal — is a valid descending sequence. That confirms the answer independently of any single step.