1. Given sets $P=\{1,|a|\}, Q=\left\{2, b^{2}\right\}$ are subsets of the universal set $U=\left\{1,2,3, a^{2}+b^{2}+a+b\right\}$, and $\complement_{U}(P \cup Q)=\{6\}$. Which of the following conclusions is correct? ( ).
(A) $a=3, b=1$
(B) $a=3, b=-1$
(C) $a=-3, b=1$
(D) $a=-3, b=-1$
$$
\begin{array}{l}
\text { I. 1. D. } \\
\text { From } \complement_{U}(P \cup Q)=\{6\} \Rightarrow a^{2}+b^{2}+a+b=6 .
\end{array}
$$

Obviously, only option D fits.