The most critical moment is choosing the reward tank. If you take a wrong tank, the only way to undo this is deleting your account and make a new.
Here are the options:
- U.S.A. tier 3 medium M2 MEDIUM TANK
- German tier 3 light tank Pz.Kpfw. 38 (t)
- U.S.S.R. tier 3 light T-46