The tone in this passage is very formal and D) Professional, because it uses the words like benevolent and Congress, and Government.
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I think that it is c just because it seems to fit the sentence
Explanation:
A witness would be someone that has experienced something at first hand, having saw something from a different perspective. An ally is someone who is acquainted with you, or someone you could trust. A witness cannot be an ally if you are against their side in some form or way. A witness can be an ally if it is your best friend or someone you trust to prove you innocent.
Basically, a witness is a neutral term that describes someone that saw something. While an ally refers to mutually acceptable.