文档介绍：Combos
Combos are powerful weapons that are triggered by a group of several turrets that are placed close together. To trigger bo you have to have a group of turrets that meets these conditions:
All turrets in the group must be very close together (less than one turrets-width apart)
All turrets in the group must have their damage upgraded to the maximum level
bo will be triggered?
This depends on which turret in the group is the first one to see an attacker and fire at it. In the first example in the list, one red turret and one green turret will fire the "Laser Rockets" combo. As this is a red bo, the red turret must be the first turret in that group to fire. This is best achieved by increasing the range of the red turret so that it is the first turret to see the ing attacker.
By changing the range of the turrets in the group you can control which one fires first, and therefore bo is triggered.
Red bos
Where a red turret is the first to fire
+ = Laser Rockets
+ = Tazer Rockets
+ + = Poison Gas Rockets
+ + = Nuke
+ + + = Napalm Rocket
Green bos
Where a green turret is the first