B

The magnetic field inside a solenoid is given by the formula:
B = \mu_0 \frac{N}{L} I
where:
- B is the magnetic field inside the solenoid,
- \mu_0 is the permeability of free space,
- N is the total number of turns of the wire,
- L is the length of the solenoid,
- I is the current flowing through the solenoid.

From this formula, we can analyze the relationship:
- The magnetic field B is directly proportional to the current I (meaning as the current increases, the magnetic field increases).
- It is also directly proportional to the total number of turns N and inversely proportional to the length L of the solenoid.

Thus, the correct statement about the magnetic field inside a solenoid is that it is directly proportional to the current (Option B).