Figure $19 < 2$ -What Change Causes the Circuit in Figure 19-2(b) to Output

Multiple Choice

Figure $19 < 2$
-What change causes the circuit in Figure 19-2(b) to output the average of the three input voltages?

A) Change the input resistors to 3.3 $\mathrm { k } \Omega \text {. }$
B) Change the feedback resistor to 3.3 $\mathrm { k } \Omega \text {. }$
C) Change to a different type of op-amp.
D) Change the feedback resistor to 10 $\mathrm { k } \Omega$