premise :- prime purchaser will not buy software that require high training cost or require user to learn unfamiliar command.
conclusion : - to be successful, software must not require user to learn unfamiliar command.
Question is asking for the inference from the passage
A - option doesn't fit with our conclusion but provide new criteria for a software to be successful.
B - so if we negate this option then the meaning of the sentence will be "commercial software that require user to learn unfamiliar command will not be more expensive than the one which don't require user to learn unfamiliar command". This is in contradiction to the premise because cost of training user is very high in case of the former.
C - we know that prime purchaser will buy a software with no unfamiliar command and thus the software be successful. this is our conclusion too.
D - out of scope; we don't have any information about the given condition.
E - out of scope; we don't have any relation between difficulty in learning a software and the cost of that software.
Hope this helps,
kudos,
Hemant













