$144\,x^2 \,- 16 = $   ?

$(12x+4)^2$ $(12\,x^2+4)(12\,x^2-4)$ $(12x+16)(12x-16)$ $(12x+4)(12x-4)$

$121\,x^2 \,- 64 = $   ?

$(121x+64)(121x-64)$ $(11x+8)(11x-8)$ $(11x+64)(11x-64)$ $(11x+8)^2$

$100\,y^2 \,- 49\,x^2 = $   ?

$(10\,y^2+7\,x^2)(10\,y^2-7\,x^2)$ $(100y+7x)(100y-7x)$ $(10y-7x)^2$ $(10y+7x)(10y-7x)$

$144\,x^2 \,- 121\,y^2 = $   ?

$(12x+121y)(12x-121y)$ $(12x+11y)^2$ $(12\,x^2+11\,y^2)(12\,x^2-11\,y^2)$ $(12x+11y)(12x-11y)$