2. Among the following four equations:
$$
\begin{array}{l}
3 \sqrt{\frac{3}{8}}=\sqrt{3+\frac{3}{8}}, \\
\sqrt{19-6 \sqrt{10}}=\sqrt{10}-3, \\
1 \lg^{2} 15=2 \lg 15, \frac{2^{\mathrm{n}+4}-2\left(2^{\mathrm{n}}\right)}{2\left(2^{\mathrm{n}}+3\right)}=\frac{7}{8}
\end{array}
$$

The number of incorrect ones is ().
(A) One.
(B) Two.
(C) Three.
(D) Four.
$A$