Answer:
B. resolve
Step-by-step explanation:
The signal words are the ones that help the reader follow the lecture in an effective way, they don't permit him to get lost in between the ideas presented. In other words, they connect the ideas presented in the text.
In this case a problem-solution signal word is used to connect a problem with it's solution. Resolve is the only one that makes that connection as it refers to a settle that is solved.
The other options are more suitable for cause-effect.