All of them are independant agencies.
The General Services Administration or GSA is an independent agency which is set up in the US by the United States government established in 1949 in order to help in managing and supporting the basic functioning of federal agencies.
GSA supplies different products as well as communications for U.S. government offices and also provides transportation and office space to federal employees, as well as develops government-wide cost-minimizing policies and also other related management tasks.
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