(15) 1 Represent the set using the roster method: $A=\left\{x \left\lvert\, x=\frac{a}{|a|}+\frac{|b|}{b}+\frac{|c|}{c}+\frac{a b c}{|a b c|}\right., a, b\right.$, $c \in \mathbf{R}, a b c \neq 0\}$ is . $\qquad$