When the current passes through the filament, it get heated to incandescence and give light while the connecting wires are not heated because:
A) The connecting wires are good conductors of heat while filament is a bad conductor.
B) The connecting wires are of low resistance while filament is of high resistance.
C) The density of connecting wires is less than that of filament..
D) The connecting wires are bad conductors of heat while filament is a good conductor.

Hint: when current passes through filament the only thing which converts electrical energy into heat and light energy is resistance. If filament would have been a good conductor of electricity, it would never have glown to give light. Also filament is a good conductor of heat. But the light and heat is produced due to electricity therefore the cause of light is resistance.

Complete answer:
When the current passes through the filament, it gets heated to incandescence and gives light because the filament is of high resistance. When current passes through a bad conductor of electricity, the energy is converted in some or other way either in heat or light. Here, the electricity is converted in light and heat due to high resistance offered by the filament. The connecting wires are good conductors of electricity therefore light or heat is not produced through it. The work of wires is to conduct electricity with minimum loss. So wires should be good conductors.

The filament bulb has tungsten as its filament and was invented due to its property to conduct electricity with giving light as by product. Tungsten having high resistance, then too can complete an electrical circuit giving light and without breaking. Materials having less resistance are used for carrying current for appliances while some materials having high resistance are used for heating or lighting purposes. The materials in conducting wires are metals which can easily conduct electricity. Appliances like geysers, heaters etc. use materials having high resistance.

Note: A filament bulb completes the electrical circuit which means the filament can conduct electricity. So it is not a bad conductor. The heating and lighting effects are produced electrical circuits only when current passes through materials having high resistance. So, the filament bulb is a good conductor but has high resistance.