Answer:
Options B and C.
Step-by-step explanation:
Difference of squares is defined as
[tex]a^2-b^2[/tex]
where, a and b both area real numbers.
[tex]y^4+9\Rightarrow (y^2)^2+3^2[/tex]
It is sum of squares.
[tex]9x^2-16\Rightarrow (3x)^2-4^2[/tex]
It is difference of squares.
[tex]m^6-25\Rightarrow (m^3)^2-5^2[/tex]
It is difference of squares.
[tex]m^7-1\Rightarrow m^7-1^2[/tex]
It is not a difference of squares.
Therefore, the correct options are B and C.
