1. If an $n$-faced polyhedron has $m$ faces that are right triangles, we say that the polyhedron's straightness is $\frac{m}{n}$. If an $n(n \geqslant 4)$-faced polyhedron has a straightness of 1, and the number of edges is $k$, then $n$ and $k$ should satisfy ( ).
(A) $k=3 n$
(B) $k=\frac{3}{2} n$
(C) $k=\frac{4}{n} n$
(D) $k=2 n$
-.1.B.
Since the straightness of an $n$-faced polyhedron is 1, all its $n$ faces are right-angled triangles. Also, because each face of the $n$-faced polyhedron contains three edges, and each edge belongs to two faces, we have $2k = 3n$, which means $k = \frac{3}{2} n$.