Factoring DOTS, SOTC and DOTC

What are the factors of  $x^2-81$  ?

•  $\left(x+81\right)\left(x-81\right)$  

•   $\left(x-9\right)\left(x-9\right)$  

•  $\left(x-9\right)\left(x+9\right)$  

What are the factors of  $4m^4-25n^2$  ?

•  $\left(4m^2+25n\right)\left(4m^2-25n\right)$  

•   $\left(2m^2+5n\right)\left(2m^2-5n\right)$  

•  $\left(2m^4+5n^2\right)\left(2m^4-5n^2\right)$  

What are the factors of  $x^3+216$  ?

•  $\left(x+6\right)\left(x^2-6x+36\right)$  

•   $\left(x-6\right)\left(x^2+6x+36\right)$  

•  $\left(x+6\right)\left(x^2+6x+36\right)$  

What are the factors of  $27m^6-125$  ?

•  $\left(3m^2+5\right)\left(9m^4+15m^2+25\right)$  

•   $\left(3m^2+5\right)\left(9m^4-15m^2+25\right)$  

•  $\left(3m^2-5\right)\left(9m^4+15m^2+25\right)$