Some expansions may be locked until certain requirements are met. These include:
- 
  Expansions to the left of the Railway Station: build the Railway Station,
- 
  Expansions to the right of the Railway Station: build the Airport,
- 
  Expansions beyond the Bridge: buy both expansions on either side of the river near the Bridge first,
- 
  Other expansions: reach the required level.
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