It is my grandmother'eightieth birthday.该句中的序数词前为何没有the

It is my grandmother'eightieth birthday.该句中的序数词前为何没有the My grandmother"s eightieth birthday was approacing and i was Today is my grandpa's___birthday.A.the eightieth B.eightieth birthday;grandmother`s ;it`s;today;my(.) 连词成句 My grandmother's 80th birthday is( ) 序数词的一些用法Today is my second birthday.为什么不用today is my the sec My grandmother is one in the white 连词成句 It was _birthday of my mother's A.eighty B.the eightieth c,e Tomorrow is my grandmother's birthday my grandmother's 下划线,对 My grandmother's birthday is December ___(thirty) My birthday is July eighth.eighth是序数词,前面为什么不加the? 为什么my birthday is junuary fourth的序数词不加the