Because you participate in many extra-curricular activities, you are not going to get good marks this term. Students must choose between doing well academically and having and participating in many extra-curricular activities.

Because you participate in many extra-curricular activities, you are not going to get good marks this term.

This would be a valid argument, but there would need to be evidence to make it sound. However, I don't know of any evidence that can be presented to make this sound since we are talking about a unique case (an individual's personal experience). A far more reasonable argument would be:

Those who participate in many extra-curricular activities, tend to not get good marks.

Then, this is now something that almost certainly has scientific data to support or falsify.

Students must choose between doing well academically and having and participating in many extra-curricular activities.

Claim or opinion. This is not evidence that addresses the argument.