Sentence Correction

This question is from kaplan, i couldnt understand the answer. I thought technology concern is not correct.

You're right that the plural verb "concern" wouldn't go with the singular noun "technology." However, in this case, it is the "complaints" that "concern" is referring to, not "technology."

I agree with the explanation given: the most important thing to look for here is parallel construction (you can easily spot this by noticing that the sentence makes a list; all items in the list must be parallel in form).

I believe "concern" is for "complaints" not for technology......so its correct usage as complaints are plural

Yeah .. concern refers to omplaints only ,.. and hence is right.
Also choice C maintains correct parallelism .. which makes it a clear choice.