A：$1+\frac{1}{2}+\frac{1}{3}+...\frac{1}{2^k}<k+1$

B：$1+\frac{1}{2}+\frac{1}{3}+\frac{1}{2^k-1}+\frac{1}{2^{k+1}-1}<k+1$

C：$1+\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2^k-1}+\frac{1}{2^k}+\frac{1}{2^{k+1}-1}<k+1$

D：$1+\frac{1}{2}+\frac{1}{3}+\frac{1}{2^k-1}+\frac{1}{2^k}+\frac{1}{2^k+1}+...+\frac{1}{2^{k+1}-2}+\frac{1}{2^{k+1}-1}<k+1$