S is the surface of a lump of magnetic material.

Options

A. Lines of B are necessarily continous across S
B. Some lines of B must be discontinous across S
C. Lines of H are necessarily continous across S
D. Lines of H cannot all be continous across S

Explanation

To solve the question regarding the behavior of magnetic field lines at the surface of a lump of magnetic material, we need to analyze the properties of magnetic fields and their lines.

### Step-by-Step Solution:

1. **Understanding Magnetic Field Lines (B and H)**:
- Magnetic field lines (B) represent the magnetic flux density, while H represents the magnetic field strength. The behavior of these lines at the boundary of different materials is governed by certain physical laws.

2. **Behavior of B Lines Across the Surface (S)**:
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