1. Given the following 4 propositions:
(1) If $m, n$ are known numbers, the sum of the monomials $2 x^{5} y^{n-2}$ and $(m+5) x^{1 m-n+4 \mid} y$ is a monomial, then the value of $m+n$ is -3 or 7.
(2) If $M, N$ are polynomials containing only one variable $x$, with degrees 6 and 3 respectively, then $M - N^{2}$ is a polynomial with a degree not exceeding 6.
(3) If $m$ is a natural number, then the solution to the equation
$(-x)^{m+1}(-x)^{2 m-2}(-x)^{3 m+1}=x^{x+1} x^{6 m-1}$ is $x=-1,0,1$.
(4) Given that $A M, D N$ are the altitudes of $\triangle A B C, \triangle D E F$ respectively, $A B=D E, A C=D F, A M=D N$. If $\angle B A C = 40^{\circ}, \angle A B C=35^{\circ}$, then $\angle D F E=105^{\circ}$.
Among them, the number of incorrect propositions is ( ) .
(A) 0
(B) 1 or 2
(C) 3
(D) 4
-、1.D.
(1) When $m=-5, n>2$, the sum of the monomial $2 x^{5} y^{n-2}$ and 0 is still $2 x^{5} y^{n-2}$. At this time, $m+n$ can be all integers greater than -3, so statement (1) is incorrect.
(2) When $M=x^{6}+1, N=x^{3}+1$, $M-N^{2}=-2 x^{3}$. And $-2 x^{3}$ is a cubic monomial, so statement (2) is incorrect.
(3) When $m=0$, $x=0$ makes $(-x)^{2 m-2}$ and $x^{6 m-1}$ undefined. At this time, $x=0$ is not a solution to the original equation, so statement (3) is incorrect.
(4) When $D N$ is inside $\triangle D E F$ (as shown in Figure 11). It is easy to prove that Rt $\triangle A M C \cong \mathrm{Rt} \triangle D N F$. Therefore, $\angle D F E=\angle A C M=\angle B A C+\angle A B C=75^{\circ}$. Hence, statement (4) is incorrect.