The following sentences are the steps involved in proving the result `(cosx)/(1-tanx)+(sinx)/(1-cotx)=cosx+sinx`. Arrange them in sequential order from first to last.

A. `(cos^(2)x)/(cosx-sinx)+(sin^(2)x)/(sinx-cosx)`

B. `(cos^(2)x-sin^(2)x)/(cosx-sinx)`

C. `(cosx)/(1-(sinx)/(cosx))+(sinx)/(1-(sinx)/(sinx))`

D. (a) (A), (B) and (C)

(C), (A) and (B)

(C), (B) and (A)