Explanation:

The sentence is talking about a person who needs to change their ways. The correct word to fill in the blank is "ought." Here's why:

1. Use of "should": "Should" is a modal verb that expresses recommendation or obligation. It is used to give advice or to say what is the right thing to do. However, in this sentence, the speaker is not giving advice or making a suggestion. They are stating that the person needs to change their ways. Therefore, "should" is not the best option.

2. Use of "must": "Must" is a modal verb that expresses strong obligation or necessity. It is used to say that something is required or mandatory. While the sentence does express a sense of obligation, it is not as strong as "must." The speaker is not saying that the person is required to change their ways, but rather that it would be beneficial for them to do so.

3. Use of "ought": "Ought" is a modal verb that expresses moral obligation or duty. It is used to say what is the right thing to do based on a sense of responsibility or expectation. This is the best option for the sentence because the speaker is suggesting that the person has a duty to change their ways in order to improve their situation.

Therefore, the correct answer is "B) ought."