Which operation shows that polynomials are a closed system under addition?

Responses

(2x2+6x+1)+(3x2+3x+9)=(2x2+3x+1)+(3x2+6x+9)

(2x2+6x+1)+(3x2+3x+9)=5x2+9x+10

(2x2+6x+1)+(3x2+3x+9)=(2x2+3x2)+(6x+3x)+(1+9)

(2x2+6x+1)+(3x2+3x+9)=−x2+3x−8

The correct response is: (2x^2+6x+1)+(3x^2+3x+9)=(2x^2+3x^2)+(6x+3x)+(1+9)

The correct option is:

(2x^2 + 6x + 1) + (3x^2 + 3x + 9) = (2x^2 + 3x^2) + (6x + 3x) + (1 + 9)