7. If $x \in \mathbf{R}_{+}$, then the term with the largest coefficient in the binomial expansion of $(1+2 x)^{15}$ is ( .).
(A) The 8th term
(B) The 9th term
(C) The 8th term and the 9th term
(D) The 11th term
7. D.
$$
\begin{array}{l}
T_{r+1}=2^{\prime} \mathrm{C}_{15}^{r} . \\
\text { By } T_{r} \leqslant T_{r+1}, T_{r+2} \leqslant T_{r+1} \\
\Rightarrow \frac{29}{3} \leqslant r \leqslant \frac{32}{3} \Rightarrow r=10 .
\end{array}
$$

Therefore, the 11th term is the largest.