$(a)$ $A$ comb run through one's dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember,a paper does not conduct electricity.)
$(b)$ Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?
$(c)$ Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?
$(d)$ $A$ bird perches on a bare high power line,and nothing happens to the bird. $A$ man standing on the ground touches the same line and gets a fatal shock. Why?

(N/A) The comb gets charged due to friction with dry hair. This charged comb induces opposite charges on the near side of the paper bits,causing attraction. If the hair is wet or it is a rainy day,the moisture reduces friction and allows the charge to leak away,so the comb does not get sufficiently charged to attract paper.
$(b)$ Aircraft tyres are made slightly conducting to allow static charge,accumulated due to friction during landing,to flow safely to the ground,preventing sparks that could cause a fire.
$(c)$ Metallic ropes are used to conduct static electricity generated by the friction of the vehicle's body with air or road to the ground,preventing the buildup of charge that could ignite inflammable materials.
$(d)$ The bird is at the same potential as the wire,so no current flows through its body. The man,standing on the ground,creates a potential difference between the high-voltage line and the ground,causing a current to flow through his body.