Fiber$-$optic wavelength division multiplexing $($WDM$)$ technology achieves high data rates by

Group of answer choices

a$)$ Transmitting a single ultra$-$high$-$speed signal on a fiber

b$)$ Transmitting multiple signals on a fiber over multiple optical frequencies

c$)$ Sending multiple signals across multiple fibers

d$)$ Compressing data before sending it on a fiber