3. Let $0 \leqslant \theta \leqslant \frac{\pi}{2}$, then the parametric equations $\left\{\begin{array}{l}x=4-\cos \theta \\ y=1-\sin \theta\end{array}\right.$ represent the graph of $(\quad$ ).
A. Line segment
B. Part of a circle
C. Circle
D. Ellipse
3. B

From the problem, we know that the figure is represented by the equation $(4-x)^{2}+(y-1)^{2}=1 \quad(x \in[3,4], y \in[0,1])$. Therefore, it is part of a circle. Hence, the correct choice is B.