$121\,x^2 \,- \,y^2 = $   ?

$(11x+y)^2$ $(11x+y)(11x-y)$ $(11\,x^2+\,y^2)(11\,x^2-\,y^2)$ $(121x+y)(121x-y)$

$121\,x^2 \,- 4\,y^2 = $   ?

$(11x+2y)^2$ $(11x+4y)(11x-4y)$ $(11x+2y)(11x-2y)$ $(11x-2y)^2$

$16 \,- 144\,x^2 = $   ?

$(16+144x)(16-144x)$ $(4+12x)(4-12x)$ $(4+12x)^2$ $(4-12x)^2$

$100 \,- 36\,y^2 = $   ?

$(100+6y)(100-6y)$ $(10+6y)(10-6y)$ $(10+6\,y^2)(10-6\,y^2)$ $(100+36y)(100-36y)$