请选择ABCD9v(@.H3V+Y;o You will stay healthy _______ you do more exercise, such as running and walking.0x4x0[;O:b;E8L(x3a)D,@3]
A. if0x4x0[;O:b;E8L(x3a)D,@3]
B. when0x4x0[;O:b;E8L(x3a)D,@3]
C. before0x4x0[;O:b;E8L(x3a)D,@3]
D. where0x4x0[;O:b;E8L(x3a)D,@3]