Figure $18 < 1$ -What Trouble in the Amplifier in Figure 18-1(b) Could Cause

Multiple Choice

Figure $18 < 1$
-What trouble in the amplifier in Figure 18-1(b) could cause the voltage between the inverting and non-inverting inputs to nearly equal 0 V ?

A) R_i is open.
B) R_f is open.
C) The power is off.
D) There is no problem; 0 V is normal.