Which of the following would be subject to theleaststringent standard of constitutional review?

1. A state law imposing strict pollution control standards on some firms, but very lenient standards on others.
2. A state law declaring that ten percent of the state's administrative employees must be members of minority groups.
3. A state's ban on advertising that contains some sexually stimulating material.
4. All of the above would receive the same level of constitutional review.