1. The sum of all natural numbers $x$ that make the algebraic expression $y=\frac{x^{2}+11}{x+1}$ an integer is ( ).
(A) 5
(B) 6
(C) 12
(D) 22
- 1.D.

Since $y=\frac{x^{2}+11}{x+1}=x-1+\frac{12}{x+1}$, to make $\frac{12}{x+1}$ an integer, the natural number $x$ can take $0,1,2,3,5$, 11, the sum of which is 22.