问几道高中英语语法题,每道题我只给两个选项,一个是正确答案一个是我选错的.请给出正确答案并说明选择理由以及不选另一个的理

问几道高中英语语法题,
每道题我只给两个选项,一个是正确答案一个是我选错的.
请给出正确答案并说明选择理由以及不选另一个的理由,
1.service is the key to__success of_hotel.
a.the,a
b./,a
2.what's born has to die----that's___law of __nature independent on man's will.
a.a,/
b.a,the
3.rather than "instant" creativity ,scientific accomplishment is _ matter if oppertunity nd continuous effort over at least _decade.
a.the,a
b.a,a
4.milk is measured in__prints when bought over a lunch counter,but gasoline is sold by _gallon.
a./,one
b./,the
从语法的角度,不要扔下一串abc就走了,
我真的很无奈，说了情况，还是只有回答选项的，