No improvement to this sentence is necessary. It makes perfect sense on its own and sounds right. "Either" always takes an "or" else the word wouldn't make sense, as it's meant to contrast binary options.
eg.
I'm either going to eat food or drink water.
Hey!
An article is piece of writing included with others in a newspaper, magazine, or other publication. Those can be academic, laboral or just personal.
Now, the subject of an article can automatically limit the timeliness, the audience and purpose. The subject acts like a border to your article and you will have to respect that limit. For instance, every article has a subject, but it will be conditioned by the subject of the writing piece; and, when writing, you have to identify your audicience and it has to be closed relationed with your subjects, because there are some topics for specific public.
In that sense, the only aspect a subject of an article can not limit is A: effectiveness. A topic by itself does not do anything, it is the way of presenting and writing about it. In addition, there is no any way to know if the article will produce the expected effect on the readers just because of the topic.
Hope this helps!
Answer: Oona is planning to ambush the Russians.
In this excerpt, we see that Oona is instructing Negore as to how to lead the Russians. Oona states that Negore should show them the way, to where they wait in a passage up the rocks. The fact that they are hidden, and that they are waiting for the Russians to pass, along with their negative attitude towards them, implies that they are planning an ambush for the Russians.
