5 A new generation of wet FGD systems, pioneered in the mid to late 1990's, improved mass transfer, which resulted in the usage of more compact absorbers that are estimated to require 50 percent less material, compared to an older generation of wet FGD systems.

Does it follow that "The older wet FGD systems were slowly becoming unusable. "?
(a). yes (b). it is not possible to tell (c). no
(b).