\[\boxed{\text{18.\ }\text{ОК\ ГДЗ\ -\ домашка\ на\ 5}}\]
\[\textbf{а)}\ N \subset Q;\]
\[\textbf{б)}\ Z \subset Q;\]
\[\textbf{в)}\ N \subset R;\]
\[\textbf{г)}\ Z \subset R.\]