C. gather together - This is like "interview", you gather potential employees together before hiring one. D. disregard - This is like "bias", disregarding a potential employee based on race, ***, or possibly beliefs. E. dissolve - This is like "fire", dissolving them from the company.
I would say A. "Employ" means not only "to hire " but also "to put to use" (as in, "We must employ all the resources available to us." The opposite of this would be "to leave idle" or "not to use purposefully."
Idle and used are opposite concepts. There is no way around it. While something is idle it cannot at the same time be employed/used (unless it has two lives). If something is employed, it doesn't matter who is employing it or who is not; if its employed, it is not idle.