1. The number of integer roots of the equation $\left[\frac{3 x+7}{7}\right]=4$ with respect to $x$ is ( ).
(A) 4
(B) 3
(C) 2
(D) 1
Hint: $4 \leqslant \frac{3 x+7}{7}<5 \Rightarrow 7 \leqslant x<\frac{28}{3}$ $\Rightarrow$ integer $x=7,8,9$. Therefore, the answer is (B).