Answer:
The best answer is: "Global warming is a big problem that we should all do something about".
Step-by-step explanation:
The best hook for an introduction is the one which states an idea and/or thesis very clearly. The last option presents a statement and makes a point that might be developed during the course of the text. The first, second, and third sentences are all arguments and/or examples for the main idea stated, and this is noticed because these three sentences leave space for other ideas and arguments, as much as examples. Therefore, the only sentence which states a thesis is the last one.