A. Zero circulation only means that the algebraic sum of the currents surrounded by the loop is zero, which does not mean that the magnetic field on the loop is zero. Counterexamples are easy to get. For example, make a closed curve that does not surround the conductor near the live wire as an ampere loop, and the magnetic field on the loop is not zero at this time. So a is wrong;

B as mentioned above, there are two ways to close the current through the ampere loop. It is stipulated that the current coming in one way is positive and the current passing through the other way is negative. If the two are equal and the algebraic sum is zero, then the circulation is also zero, so zero circulation and no current passing through the loop are two different things. So b is wrong;

C. analyze c as above;

D. The strength of the magnetic field on the loop is not only related to the closed current, but also related to the unsealed current, which depends on all the currents around the loop, so D is wrong.