Which expression is the factorization of x squared plus 10 x plus 21 ?
A
open paren x plus 4 close paren times open paren x plus 6 close parenB
open paren x plus 3 close paren times open paren x plus 7 close parenC
open paren x plus 6 close paren times open paren x plus 15 close parenD
open paren x plus 7 close paren times open paren x plus 14 close paren