ANS:A - scaling adder

DAC has the same circuit as that of the scaling adder where each input is multiplied by the ratio of the feedback resistance to input resistance which determines its value, for example, bit 0 has Rin = 8R, bit 1 has Rin = 4R and Rf = feedback resistance = R.

Then, Vo = Rf(Vin1/Rin1 +Vin2/Rin2),
Vo = R(Vin1/8R+Vin2/4R) = (Vin1)/8 + (Vin2)/4 representing a digital signal 10 as an analog signal.