$A = \{ \frac{x}{x-1} | x \in N, (-3) < x < 5 \} = \{$

$B = \{ x | x \in N, \frac{20}{x} \in N \} = $

$C = \{ 2^{x} | x \in Z, 0 \le x \le 5 \} = $

$D = \{ x | x \in Z, x^{2} < 49 \} = \{$