Ans. is 'a' i.e. Tympanic membraneBlast or shock waveo When an explosion occurs, the explosive material produces a large volume of gas and releases a large amount of energy. It produces a 'shock wave' which spread concentrically from the site of explosion. The injuries depend on the environment in which blast occurs :-Air blast (most common) : Explosion occurs in air. There is barotrauma to air filled hollow organs. Tympanic membrane (ear drum) is most sensitive and most commonly injured. Lung is the second organ to be injured and is the most commonly injured hollow organ and most common cause of life threatening injury. Other parts injured are middle ear, cochlea, eyes, bowels, mesentery, omentum and brain. Homogenous solid organs like liver and muscles are usually not affected.Under water blast (explosion under water) : Gastrointestinal tract is injured most commonly. Lungs are also injured.Solid blast: Explosive is detonated near a rigid/solid structure and wave of energy spreads through it. If people are in contact with that rigid structure, injuries take place. The injuries are mostly skeletal; fracture of legs and vertebral column are more common. GIT damage is more common than lung.