The 2 premises tell us that people buy new computers after 4 years despite 2 things:
1. The fact that they can still perform "BASIC" functions with the old computer and
2. They are designed to last up to 10 years.
What do these 2 facts tell us?
A. This is an Opinion/Suggestion. It does not sum up the two facts above. Out of scope.
B. It gives us an exact reason "substantial functional upgrades" but there is nothing in the passage to support this. Maybe they do it, because of design upgrades as opposed to functional upgrades - OUT.
C. NEW INFO - Nothing in the passage to suggest this. For all we know people "dump their computers" after 4 years. Remember, we should not use real-world info when answering CR questions - OUT.
D. NEW INFO - Irrelevant - We are looking for something to sum-up the 2 facts above, this is taking us in a whole new direction - OUT.
E. Correct. Uses mild language, says there must be other factors, but isn't overly specific on what those factors as, as there isn't enough info in the premise to arrive at such a specific conclusion.