问题如下图：
SL的系数为啥是1/5，答案的公式和老师说的不一样。如果用老师上课说的公式可以做吗？
选项：
A. 
B. 
C. 
解释：
NO.PZ2018062004000157 The straight-line metho They have the same net income in ye5. A is correct. Apting the straight-line metho the preciation expense in ye5 will account for 1/5=20% of the totpreciable cost. Apting the units-of-proction metho the preciation expense in ye5 will account for 1200/5200=23% of the totpreciable cost. So we cthe conclusion ththe units-of-proction methowill prohigher preciation expense, leang to lower net income in ye5.老师，uints of proction metho 方法也是每年平均折旧吗？每年折旧23%?
The straight-line metho They have the same net income in ye5. A is correct. Apting the straight-line metho the preciation expense in ye5 will account for 1/5=20% of the totpreciable cost. Apting the units-of-proction metho the preciation expense in ye5 will account for 1200/5200=23% of the totpreciable cost. So we cthe conclusion ththe units-of-proction methowill prohigher preciation expense, leang to lower net income in ye5.我知道可以通过每种方法不同计算，可是为什么课上提到三种方法累计折旧都是一样的，虽然每种方法在每一年折旧费用不同。那样的话不就是都一样吗？
The straight-line metho They have the same net income in ye5. A is correct. Apting the straight-line metho the preciation expense in ye5 will account for 1/5=20% of the totpreciable cost. Apting the units-of-proction metho the preciation expense in ye5 will account for 1200/5200=23% of the totpreciable cost. So we cthe conclusion ththe units-of-proction methowill prohigher preciation expense, leang to lower net income in ye5.不是说不管用什么方法，到useful life结束之后总共的preciation都是一样的吗？
不太理解这道题的答案。 如果按照直线折旧的公式是怎么算出来1/5 的？ 残值和固定资产原值都没有提供， 用1/5 就能直接和单位折旧做对比了么？
