29 .51 Expression $x^{2}-y^{2}-z^{2}+2 y z+x+y-z$
(A) has no linear factor with integer coefficients and integer exponents.
(B) has a factor $-x+y+z$.
(C) has a factor $x-y-z+1$.
(D) has a factor $x+y-z+1$.
(E) has a factor $x-y+z+1$.
(14th American High School Mathematics Examination, 1963)