Cardinality of units in a commutative ring with unity

Question

Let A be a commutative ring with unity. A* denotes the group of units in A. Then cardinality of A* cant be

1. 5
2. 4
3. 3
4. 2

I know that there is a possibility of euler phi (n) elements in A*. So 2 &4 can be the cardinality of A*. But what about the other two options.