Problem 3

Explanation

The residents' argument is: The increase in motorcycle theft is caused by security guards not performing their duties properly.

To weaken this argument, we need to find a fact showing that the security guards are actually performing their duties properly (so the cause of the theft might be another factor, not the guards' negligence).

The option stating that security guards patrol regularly shows that the guards have been doing their job (patrolling). This contradicts the residents' claim that the guards are not performing their duties properly.

Therefore, the fact that guards patrol regularly weakens the residents' accusation.