The argument made in the text is the last line of the text.
A – Wrong
This would, in contrast, weaken the argument. Since the argument made is that water cannons should be used when appropriate, this statement contradicts the argument.
B – Wrong
This is irrelevant and does not strengthen the argument.
C – Wrong
This weakens the argument made in the text. If tear gas or rubber bullets are equally as effective as water cannons, then these methods should adopted instead of water cannons.
D – Wrong
This mentions how expensive water cannons can be so weakens the argument.
E – Correct
If the public supports the use of water cannons, then this strengthens the argument.