Word choice is tied to vocabulary, so the first trick is to increase your vocabulary frequently. Not only knowing the words, but use them. Implement them in a way that makes your writing carry the message across more effectively. For example, instead of using “I like” say “I admire” or “I adore”.
Tone can tie to word choice. Even though both word choice and tone are important in writing, tone should not change without a good reason. For example, if I am writing about a happy time, I would make my word choice really display my enjoyment (if that doesn't make sense read over your writing and it should sound like the person is in a good mood.). If I were writing about a memory when I was in a good mood and then suddenly I died or something tragic I would also display that using word choice. Since the reader cannot see your face, word choice and tone are The only way you can display your mood and really make sure the reader understands what you are saying easily
I'd say the correct answer is B, because 'in the desert is part of the subject/noun 'canyon', and modifies it, that is, refers to it, describes it in more detail.
