A magnetic needle behaves like a magnetic dipole with magnetic moment $\vec{m}$.

In a magnetic field $\vec{B}$, a magnetic dipole can experience:

• Torque: $\vec{\tau} = \vec{m} \times \vec{B}$ This tends to align the needle along the field.
• Force in a non-uniform magnetic field: $\vec{F} = \nabla(\vec{m} \cdot \vec{B})$ If the field is non-uniform, the two poles of the needle experience unequal magnetic forces, producing a net force.

Therefore:

• Since the field is non-uniform, the needle experiences a force.
• Also, unless it is already exactly aligned with the field, it experiences a torque.

Hence, the correct option is: $\boxed{\text{D: a force and a torque}}$

Comparison with stored correct answer:

• Stored correct answer: $\text{D}$
• Derived answer: $\text{D}$
• They match.