3×5=____5×6=____2×5=____5×5=____4×5=____
设等比数列{an}的前nn项和为sn,已知a1=2012,且an+2an+1+an+2=0n∈N*,则s2013=( )
thirsty her grape since produce
We have an English test _________ July 5th each year.
下列关于商品谷物农业叙述正确的是