The electric iron

Which explanation is the right one?

a) A bimetallic strip is built into the electric circuit of the iron, which buckles when it heats up. When it gets too hot, the strip bends far enough for the circuit to open up, so that the heating element does not produce any further heat. As soon as the strip cools down again, it bends back and the circuit closes again. In this way the iron stays at a steady temperature.

b) The soleplate of the flatiron can only reach a maximum temperature. Iron cannot get warmer than around 200 °C. When the soleplate reaches this temperature, the small light goes out for notification. Therefore the flatiron stays at a steady temperature that is exactly right for ironing.

c) A specific fuse is built into the circuit of the iron, which blows when the temperature reaches a threshold. The circuit is disrupted. Therefore the little lamp does not burn anymore and the heating element does not produce any further heat. In this way the iron stays at a steady temperature.

d) A metal stick is built into the circuit of the flatiron. When the stick is exposed to heat, it contracts. When it gets too hot, a gap opens up in the circuit, so that it is disrupted. The heating element does not produce heat anymore. As soon as the stick cools down again, it expands and the circuit closes again. In this way the iron stays at a steady temperature.