Ex$1.(4$points$)$ Determine the cardinality of each of the following sets.

a$.$ A $\backslash$times B$,$ where A $=\{$a$,$ b$,$ c$,$ d$,$ e$\},$ B $=\{$x$\}.$

b$.\{\{\{$a$,$ b$,$ c$\}\}\}$

c$.\{\{\}\}$

d$.\{\{\},,\{\{\}\},$ a $,\{\}\}$