A 16-year-old with a GDL probationary/intermediate license has been licensed for three months. According to typical GDL rules, which of the following passengers can they legally transport without an adult supervisor?

1. Three of their high school friends.
2. Their 17-year-old sibling and 15-year-old cousin.
3. One friend who is under 21 years of age.
4. Their parent and two of the parent's friends.