Sega Hot Rod "select key"

Hello everyone.
I managed to get my favorite Arcade game "Sega Hot Rod" running on MAME 0.184 on my Windows PC.

I can start and play the game, but after every stage you have the chance to buy some extras for your car.
I can't figure out which key on the keyboard is used to select an item. Since you only got 10 seconds to buy something it is kind of hard to find out.
Does anyone know?
I am using the default keyboard set by the way.

Thanks in advance

Gerald

Found the answer on my own!
Pretty simple. Just press the key for the throttle (left CTRL in my case) for 1-2 seconds.