What happens to iron filings when they are near a solenoid with current flowing through it?

When the switch in the circuit is closed, an electric current flows through the solenoid. This current creates a magnetic field around the solenoid, turning it into an electromagnet. Iron filings are ferromagnetic materials, which are strongly attracted to magnetic fields.

Therefore, the iron filings will be attracted to the solenoid.

The correct option is D.

$$\boxed{\text{D. They will be attracted to the solenoid}}$$