Simplify the following text for a Grade 6 native English-speaking person.
Original: At the end of 2005 , Speed drove the first three races of the new A1 Grand Prix series for A1 Team USA , achieving a best result of fourth in the Feature Race of the 2005 â `` 06 A1 Grand Prix of Nations , Portugal , held at the AutÃ dromo do Estoril .
Simplified: At the end of 2005 , Speed drove the first three races of the new A1 Grand Prix series for A1 Team USA .