The task is connecting MacPro with 3 monitors, so I ordered Samsung monitors which come with Display, DVI and VGA port on each monitor.
MacPro 2010 comes with two mini-Display ports and one Dual-link DVI. The first trial is to convert mini-Display port to DVI using this mini-Display port to DVI adapter.
However, because of insufficient power, only 2 displays are working (the ones from mini-Display ports)
So I have to order mini-Display port to Display port cable from CircuitAssembly to make these three screens work. Now everything is perfect, I can drive 3 monitors simultaneously.