初中英语数词的用法单选题

--- Do you know the boy________ is sitting next to Peter?
--- Yes. He is Peter’s friend. They are celebrating his ________ birthday.

A．who; ninth

B．that; nineth

C．/; nineth

D．which; ninth

Our teacher asked us to write a _________ letter in English this morning.

A．ninety-word	B．ninety-words
C．ninety word	D．ninety words