The argument of the passage is the last line. According to the argument, it is better for young people to show aggression through rugby than by violent behaviour. (Hence rugby should not be banned).
1 – Correct
Since it is important for young people to channel their aggression in a controlled manner, activities such as rugby are important. However, if it is unfeasible for the school to replace rugby with other activities, rugby is the only activity by which young people can channel their aggression in a controlled manner. Therefore, this strengthens the argument as it suggests that it is important for rugby to be present in school.
2 – Correct
If aggression is a natural and unavoidable behaviour, it should be channelled in a controlled manner rather than channelling it through violent behaviour. Therefore, rugby is important for young people to channel their natural and unavoidable aggression. So this strengthens the argument.
3 – Wrong
This suggests that only rugby and no other sport can cause head or spinal injury. This weakens the argument as it suggests that rugby is the most dangerous sport and hence should be banned.
So D is the answer.