See, when you encounter a pronoun, just be very clear what is that pronoun refering to. If you are not clear, then there is something wrong in that question.
"They", here can refer to eith Stations or Journalist. Hence, work on choices that solve your problem.

A. Ignore. Use of they is unclear.
B Ignore, same as A.
C. Same as A. Ignore.

D and E should be the one you are unclear with.
Do you know the real usage of "that". Well, I am not carrying the material with me that can be referred right now. So, I am giving you the direction, please use internet and try to dig into it. 99% reason for usage of THAT is "it is used to refer the 'essential meaning' of the sentence." Something, you can not do without in the sentence.

Hence, I would pick D.

Yes. I was confused between D and E.

Does'nt D have an ambigous 'they' in it??

Hence I was looking to E as the answer. Would like to get this one clear.

I understand that 'that' introduces a restritive clause, which is essential for completing the sentence.

The 'they' in answer choice D isn't ambiguous. It clearly refers to the power stations because it says they could be made safe. In the first part of the sentence talks about journalists opinions, but power stations safety.

Danielle,

Could you please explain the problem with choice E?

Can "will" go with "could" in choice D?

Thanks

Choice E is incorrect because it actually writes out 'power stations', which is less concise than putting a pronoun there like D. In addition 'would' is wrong, because it is conditional. The sentence is talking about what will happen in the future, so the verb has to be in the future tense, hence 'will be' is correct.