a) Hot bitumen
b) Bituminous felts
c) Mastic asphalt
d) Metal sheets

Answer: a
Explanation: Due to its physical nature, hot bitumen remain flexible even after cooling and it is placed on the bedding of concrete or mortar. This material should be applied with a minimum thickness of 3 mm. Whereas Mastic Asphalt is a semi rigid material and it forms and excellent impervious layer for damp proofing.