Because you are so familiar with your document, other people are better at pointing out it’s flaws.
Answer? = B.) well
It completes the sentence so that it makes sence and adds that missing modifier.
Our Solar System has nine major planets. Only one is knows to have intelligent life.
Or if it must be in one sentence:
Our Solar System has nine major planets, but only one is knows to have intelligent life.
The news could very easily spread false news/propaganda. News stations care more about getting views then anything. News can be seen to be negative.