A -INDIVIDUAL GROUNDS B -THROUGH AN ISOLATION TRANSFORMER C- ONE COMMON GROUND D- NO MORE THAN 3 GROUNDS E- IN PARALLEL?
The national electric code states where no ground is available, you have to replace a two prong receptacle with another two prong receptacle. An exception is made for installing a GFI receptacle (3 prong) in the place of the 2 prong. Be aware, there still won't be a ground available for your equipment. Those are the only legal options you have besides rewiring to provide a ground. That is assuming there is no ground available at the box and chances are there is not. You are not allowed to run a ground wire separately to a water pipe or ground rod as the non trained hacks are going to try to tell you. That is a code violation. All conductors for a circuit must be run together according to the National Code. To convert your house or maybe just certain rooms, call a real electrician or pull new wires to the receptacles.
Ideally you want one common ground for everything. With multiple grounds, you might get voltage differences between ground points (if there are significant currents flowing) which can affect measurements. For noise isolation, some prefer to have separate grounds for power, analog and digital circuits which can be okay as long as you tie them together at a single-point ground.
