1. Given the set $P=|x| \cdot x^{2}=1 \mid$ and $Q=\{x|m x=1|$, if $Q \subset P$. Then the number of real values that $m$ can take is ( ).
A. 0
B. 1
C. 2
D. 3
1. D

Since $P=\{-1,1\}, Q \subset P$, $Q$ could be $\phi, \{-1\}, \{1\}$. When $Q=\phi$, $m=0$,
when $Q=\{-1\}$, $m=-1$,
when $Q=\{1\}$, $m=1$,
thus $m$ has 3 values: $0, -1, 1$.