For those who work with their brains, exercise is _____.[ ]

A. of very value

B. of great valuable

C. great valuable

D. very valuable

某建筑企业购人一台打桩机械，该机械原价20万元，预计使用年限为5年。根据企业会计准则及其相关规定，按年数总和法计提折旧，该打桩机械第二年的折旧率为（）。

A.10%

B.20%

C.25%

D.26.67%