Thelma's birthday .......... (to fall) on Monday next month.
- is going to fall
- will fall
- is falling
- falls
📝 Detailed explanation
We often use Present Simple to talk about future events that are fixed in schedules or calendars. Examples:- The train leaves at 7.
- My birthday falls on Monday.
Therefore the correct sentence is: Thelma's birthday falls on Monday next month.