根据句意，选用所给词的适当形式填空
country     twelve       they         west       happy    
What do you want to buy for his ____________ birthday？A toy car.
We own the blue house while the yellow one is _______.
To eat in a ___________ restaurant is quite different from in a Chinese one.
China is one of the biggest _____________in the world.
How _________ the children are singing and dancing in the classroom.