$A=\left\{x:x=3n\text{i}n\in \mathbf{N}\right\}$  

$B=\left\{x:x^2=16\right\}$  

$C=\left\{x:x=\frac{1}{5n}\text{i}n\in {\mathbf{N}}_{+}\right\}$  

$D=\left\{x:x^3-5>22\right\}$  

$E=\left\{7^x:x\in \mathbf{N}\right\}$  

$F=\left\{x:\frac{1}{x}\ge \sqrt{2}\right\}$  

$G=\left\{x:x+x^2\le 4\right\}$