Topic: Group verb,

Best Answer Explained in Below-:

The phrase "you should take up swimming" is the most appropriate choice because "take up" is a phrasal verb commonly used to mean beginning a new activity or hobby. This expression conveys the idea of starting something new, such as engaging in swimming as a regular practice.

In contrast, the other options do not fit well in this context:

- **A) start up**: This phrase is generally used in the context of initiating a business or project rather than personal activities or hobbies.

- **B) get up**: This usually refers to rising from a seated or lying position, and it does not pertain to starting an activity like swimming.

- **C) get off**: This expression typically means to leave a mode of transportation or to disengage from a discussion or situation. It lacks the connotation of starting a new activity.

By using "take up," the sentence effectively communicates the encouragement to start swimming, making it the correct choice among the provided options.