$1 \cdot 74$ Simplify $\sqrt{4+2 \sqrt{3}}+\sqrt{4-2 \sqrt{3}}$ to get
(A) $2 \sqrt{3}$.
(B) $2 \sqrt{2}$.
(C) 2 .
(D) $2 \sqrt{3}-1$.
(China Beijing Junior High School Mathematics Competition, 1993)
[Solution]
$$
\begin{aligned}
\text { Original expression } & =\sqrt{(1+\sqrt{3})^{2}}+\sqrt{(1-\sqrt{3})^{2}} \\
& =(1+\sqrt{3})+(\sqrt{3}-1)=2 \sqrt{3} .
\end{aligned}
$$

Therefore, the correct choice is $(A)$.