The statement "Comitatus was a bond between an Anglo-Saxon lord and his retainer," is true. Option A is correct.
In ancien times, the Latin term Comitatus refered to an armed escort or retinue. The term was employed particularly in the context of Germanic warrior culture, for a warband tied to a leader by an oath of fealty.
In other words, it is a leader, especially in pre-Christian Germanic cultures like Anglo-Saxon England and Viking Age Scandinavia.