Answer:
C. III and IV only
Explanation:
Kirchhoff's voltage or loop law says that the sum of voltage drops around a loop must equal the sum of voltage gains. This is based on the fact that energy must be conserved.
Therefore, statements I and II are both true.
Statement III is true, however, it is not part of Kirchhoff's voltage law. Instead it is Kirchhoff's current law.
Statement IV is false. If the voltage gain is zero, then the voltage drop must also be zero.