An adverb clause is a dependent clause which cannot exist on its own, it has to be a part of the main, independent clause. So, having that in mind, the only dependent clause among these examples is 'when you return from California'. Therefore, the correct answer is B.
Dear ______,
I was just writing this to express my gratitude and appreciation! Thank you so much for everything you do! It really means a lot to me and I don't know how I can ever repay you! I am thankful for how you ______, ________, and ______.
Then when you get to the body paragraphs you could repeat one reason you were thankful for them and explain more deeply in each paragraph. Make sure to use a lot of positive adjectives to make it more wordy! Then close of in a closing paragraph. For example....
Again thanks so much for everything! Your kindness means everything to me and everyone around you!
I wish you all the best and more,
_____________
Answer:
2. It is about changes over time in the Quino Checkerspot butterfly population.
Explanation: