Maybe, but try to log out and login again, might can help. And are you sure you don’t see these? (the circled one)
http://angrybir.de/1kOGfDd

If you love to play mario kart series, you will love to play this game too. That’s what happens to me :D

Facebook too actually. Every time you finish an event/race, you will see your scores and stars you get. Under the energy meter, there’s your high score and tap the “see your friends scores'”. And then, just login […]

I found that tilt controls is sensitive on my device. Is there anyway to reduce the sensitivity?

For touch controls, just press and hold right or left depending the direction you want to turn. That is easy right ; )

‘Tired player’ can make us not too addicted as well. Sometimes I feel it’s annoying, but this is a good idea for me. Toreadors’ idea is good too actually, we can save our money if it was included in the game : )

To pass it, you have to hit your car to an opponent. I finally pass most of the challenges (except that ‘beat your friend’s high score’ bescause I don’t have Facebook :P )