问题
Busy as Tom is, exercise has always been______his work.
A:as a part of his life much as
B:as much a part of his life as
C:as much as a part of his life
D:so much a part of his life as
B:as much a part of his life as
C:as much as a part of his life
D:so much a part of his life as
正确答案是：
