Stair treads must be
resistant. this is especially important for outside stairs exposed to the elements or stairways exposed to wet conditions

Slip Resistant.

By having slip resistant stairs, especially stairs that are exposed to the elements, there will be lesser risk of accidents that may occur. Stair treads alone can help with slip-resistance, but slip-resistant paint could also help in making stairs or stairways safer.  

It is also recommended to do regular cleaning maintenance to avoid growth of slippery substances that could affect the stairs traction. This would include stairways that have handrails as even the handrails are constantly exposed to the elements too. Regular maintenance will also help with the stairs visibility in most cases.

the correct answer is d