Design a case structure that tests the month variable and does the following:

1. If the month variable is set to 1, it displays “January has 31 days.”
2. If the month variable is set to 2, it displays “February has 28 days.”
3. If the month variable is set to 3, it displays “March has 31 days.”
4. If the month variable is set to anything else, it displays “Invalid selection.”