- A thermos flask is designed to minimize heat transfer by conduction, convection, and radiation. - To minimize heat transfer by radiation, the surfaces of the inner and outer glass walls are made shiny (often silvered). Shiny surfaces are poor emitters and poor absorbers of thermal radiation. - Statement A is correct: Vacuum between walls minimizes conduction and convection; glass is a poor conductor. - Statement B is correct: The glass walls have shiny surfaces to reduce radiation. - Statement D is correct: Cork or plastic supports minimize conduction through the neck. - Statement C is incorrect because the shiny inner wall surface is designed to radiate a poor amount (low emissivity) of heat, not a "good amount". While the outer wall would absorb some radiated heat, the primary mechanism to reduce radiative transfer is the low emissivity/absorptivity of the surfaces.