1. Given the system of inequalities about $x$
$$
\left\{\begin{array}{l}
\frac{2 x+5}{3}-x>5, \\
\frac{x+3}{2}-t<x,
\end{array}\right.
$$

has only five integer solutions. Then the range of $t$ is ( ).
(A) $-6<t<-\frac{11}{2}$
(B) $-6 \leqslant t<-\frac{11}{2}$
(C) $-6<t \leqslant-\frac{11}{2}$
(D) $-6 \leqslant t \leqslant-\frac{11}{2}$
1. C.

It is known that the solution set of the system of inequalities is
$$
3-2 t<x<20 \text {. }
$$

Since the system of inequalities has only 5 integer solutions, therefore,
$$
14 \leqslant 3-2 t<15 \Rightarrow-6<t \leqslant-\frac{11}{2} \text {. }
$$