Explanation:

Let’s break this down, blank by blank—especially focusing on the last one, since that’s the question.

1. The Crosses, the village (1) ______ Vasili Andreevich lived…

- You’d need “where” here. It’s giving the location where he lived.

2. …passed the blacksmith’s hut, (2) ______ last in the village…

- “the” works. It identifies the very last hut.

3. The tracks left by the sledge-runners were immediately (3) ______ by snow…

- “covered” should go here. The tracks are covered by snow.

4. …the road was only (4) ______ by the fact…

- “marked” or “indicated” could fit, but we don't need to focus on that.

5. …the line where sky and earth met could not be (5) ______.

- Here’s the thing. The sentence is in passive voice, and we need a past participle to finish it. Here’s what the options mean:

- Option 1: seen —This fits naturally. “Could not be seen” is standard English for describing something invisible.

- Option 2: seeing—Wrong tense/form. You can’t say “could not be seeing.”

- Option 3: saw—Wrong form; “saw” is simple past, doesn’t fit here.

- Option 4: see—Wrong form; you can’t follow “could not be” with the base verb here.

So your answer is Option 1: “seen.”

That’s the natural, idiomatic choice. Every other option just sounds off or ungrammatical. Good instinct!