The cover of a solar cooker is made of glass because:
A) A glass is a good conductor of heat.
B) Food being cooked can be seen through it.
C) Glass does not absorb heat radiation. Therefore energy is saved.
D) Glass allows sunlight into the cooker but does not allow heat radiation out of it.

Hint: Solar cooker is a device used to cook food using direct sunlight converted to heat. It has no cost to operate or uses no fuel or air or electricity to cook food. The material used to make a solar cooker is glass, allowing the light energy to pass through and cook food.

Complete step by step answer:
A box cooker has a transparent glass, and it may have additional reflectors to concentrate sunlight into the box. One or more glasses of shiny metal or foil-lined material may be positioned to bounce extra light into the interior of the oven chamber. Cooking containers and the inside bottom of the cooker should be dark black. Inside walls should be reflective of reducing radiative heat loss and bouncing the light towards the pots and the dark bottom, which contacts the pots. The box should have insulated sides. Thermal insulation for the solar box cooker must withstand temperatures up to without melting or out-gassing. There are four basic solar cookers: panel cooker, box cooker (sometimes called box ovens), parabolic cooker, and tube cooker in a solar cooker. Infrared radiation emitted by sunlight is used in heating a solar cooker. The Glass sheet is responsible for cooking because it captures the heat inside the solar cooker.

Hence, the correct option is (D).

Note: Basically, solar cooker work on the three main principles i.e.
i) Concentrating sunlight
ii) Converting light energy into heat energy
iii) Trapping heat energy
There are different types of solar cookers using other cooking methods, but most of them follow these principles.