Answer: The sentence that has a forceful tone is the first one: Think it over!
Explanation: A sentence with a forceful tone is one in which the author expresses extreme power and strength. The sentence "Think it over!" shows a forceful tone because it has been written in the imperative mood, a mood mainly used to express an order or a command. Moreover, this sentence includes an exclamation point at the end, which indicates that the speaker is shouting because he is experiencing a strong feeling, such as anger.
