Lalli

means unbelievable or perplexing, and there is nothing in the given sentence to suggest that ball lightning means either of those things.

means literally without comparison. The second part of the sentence after the semicolon describes the ball lightning as having a brief dazzling display; that does not provide any information about whether ball lightning can be compared to anything else.

An object that is _______has only the illusion of depth but may be two-dimensional. This does not relate to the description of ball lightning in the sentence.

The prefix poly- means "many," and polymorphous means having many shapes or stages. There is no indication in the given sentence that ball lightning has multiple shapes or stages

In this sentence, the punctuation is your best guide, drawing attention to the word that. That carries an implication of so that or in order that. It tells you to look for a cause and effect. Both bits of information in the sentence up to the blanks signal the same cause: The traveler had no companion but his staff and he paused to exchange a word with the innkeeper. The effect of having no companion is the need to ward off loneliness, and that is the answer choice.

The sentence insinuates that the wayfarer has a long way to travel, so fatigue may seem like a reasonable word to complete this sentence. However, the clue that the wayfarer stops to talk to the innkeeper does not relate to fatigue.