Which of the following terms is NOT closely associated with the Industrial Internet of Things $($IIOT$),$ which is the billions of industrial devices that are equipped with sensors$,$ connected to wireless networks, and gather and share data?

a$)$ Fourth Industrial Revolution $(4$IR$)$

b$)$ Machine$-$to$-$Machine $($M$2$M$)$

c$)$ Rapid application development $($RAD$)$

d$)$ Industry $4\mathrm{.}0$