What must tenants refrain from doing according to their duties?

Tenants have various responsibilities to uphold a harmonious tenancy, and one crucial duty is to avoid using the property for illegal purposes. Engaging in any illegal activities can lead to serious consequences, including eviction, legal action, or damage to the landlord's property. Such actions violate the lease agreement and compromise the safety and wellbeing of surrounding tenants and neighbors.

While the other options relate to common tenant duties, they do not capture the broader legal implications that accompany unlawful conduct. For instance, making repairs without permission could lead to disputes regarding the property condition or tenant modifications. Paying rent on time is a standard requirement, crucial for maintaining the leasing relationship, but does not involve legality. Subletting the premises might require permission from the landlord, although it doesn't inherently breach laws unless done in violation of the lease terms or regulations. Therefore, the prohibition against using the property for illegal purposes is a paramount responsibility that safeguards not only the landlord's interests but also the integrity of the community.