Incandescent bulbs are designed by keeping in mind that the resistance of their filament increases with the increase in temperature. If at room temperature. 100 W, 60 Wand 40 Wbulbs have filament resistances $$R_{100}, R_{60}$$ and $$R_{40}$$, respectively, the relation between these resistances is

A

$$\frac{1}{R_{100}} = \frac{1}{R_{40}} + \frac{1}{R_{60}}$$

B

$$R_{100} = R_{40} + R_{60}$$

C

$$R_{100} > R_{60} > R_{40}$$

D

$$\frac{1}{R_{100}} > \frac{1}{R_{60}} > \frac{1}{R_{40}}$$