Firstly, the formula of magnetic field intensity in Maxwell's equations is that the annular flow of magnetic field is equal to the sum of conduction current and displacement current. This problem limits the steady magnetic field, that is, the influence of displacement current is not considered.

Let's start with B: It can be seen that B and C are inverse propositions. The magnetic field is excited by the current in the whole space, not just the current in the closed curve. If there is no conduction current in the closed curve, we can say that the loop flow from H to the closed surface is 0, but we can't say that the curl of each point is 0. In most cases, even if there is no conduction current in the closed curve, the current distribution outside the curve is asymmetric, and the magnetic field of each point on the closed curve is not zero. As long as the magnetic fields of each point on the curve are added up, the H circulation is zero. This is the difference between the integral form and the differential form of physical formulas. For general physics, only integral form is required, so there is doubt about this option. This also shows that when solving problems with Ampere's loop theorem, only the problem of high symmetry of current distribution can be solved (the Gauss theorem of electric field is similar). If we want to solve the asymmetry problem, we must solve the definite solution in differential form. In most cases, Poisson equation is solved to get series solution.

For a and d, the concepts of magnetic induction intensity b and magnetic field intensity h are confused.

Let's start with A: The magnetic field intensity H includes not only the meaning of current exciting the magnetic field in space, but also the effect of medium on the magnetic field. H is not only related to the conduction current, but also related to the medium in which it is located. If the direction of the magnetic permeability gradient ▽ μ of the medium is not perpendicular to the direction of the magnetic field intensity H, then the magnetic field intensity is not only related to the conduction current, but also related to the distribution of the magnetic medium. This option is correct if it is added to an infinitely uniform medium.

Finally, D: If there are two media in space, the tangential component of H is discontinuous at the interface of magnetic media, so the H flux is not equal to the B flux. If it is changed to B flux, this option is correct.

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General physics of cheng he.

Electromagnetism, Liang Canbin.

Electrodynamics, by Guo

Methods of Mathematical Physics written by Yao Zheng.