先算：1/2+1/4+1/8=7/8,
1/3+1/6+1/5=1/2+1/5=7/10,
A=1+1/2+1/3+1/4+1/5+1/6+1/7+1/8
=1+(1/2+1/4+1/8)+(1/3+1/6+1/5)+1/7
=1+7/8+7/10+1/7
因为:1/7>1/8
则：2