下列运算正确的是 $($　　 $)$

A． $a·a^4=a^4$B． ${\left(a^2\right)}^3=a^6$

C． ${\left(a^2{b}^3\right)}^2=a^4{b}^5$D． $a^6÷a^2=a^3(a\ne 0)$