An effort to upgrade the oil machinary

[JalpanP687]

[redacted]

I saw the original question somewhere whose source is not known to me. So I've changed the context but tried to kept the structure of the question to avoid any copyright violations as per forum rules. My purpose is to learn and clear the concept tested in such question. My question is what is the difference between answer choice A and C ? To me, it seems placing of words is different. Being non-native speaker I was confused between A,C and E. Can E be the answer and why ?

Thank you !

[RonPurewal]

I saw the original question somewhere whose source is not known to me.

...then, sorry, but we can't use it.

more importantly—why in the world would YOU ever use problems from an unknown source? that's a terrible idea.