Final answer:
The sentence should be completed with 'neither supported by government funds,' indicating that both statements are untrue for NRECA.
Step-by-step explanation:
The correct way to complete the sentence is:
NRECA is neither supported by government funds nor is it an agency of the Federal Government.
In this sentence, the student is meant to use the correlative conjunction 'neither... nor' to indicate that two statements are both not true. The National Rural Electric Cooperative Association (NRECA) is the organization in question, and it is being clarified that it does not receive governmental funding, and it is not a governmental agency. Such grammatical structures are important for constructing clear and concise sentences in English.