根据以下内容，回答下列各题。 The Esky, a great Australian invention--its about as important

to the Australian household as a BBQ(吃烧烤的野餐). How else would.we move our carefully prepared food and drink around without having it spoilt.Though it is a regular problem with Esky, you also need to plan. If you haven t had a freeze pack, then you 11 need to go out and buy a bag of ice (maybe even several bags of ice). Get a Portable Mini Fridge and you 11 save on the bags of ice as well as a good deal on cleaning time. The Portable Mini Fridge requires a 12V DC supply, and you 11 find this thermo electric cooler the best thing invented since sliced bread (near enough anyway). One thing this car fridge has over your average Esky--itll warm to 60--65℃... and it does all this with-out any environmental pollution. Apart from basic cleaning, this thermo electric warmer is largely non-wearing and maintenance-free. At last, an affordable mini fridge for your car or boat will help save those green vegetables or fruits better, also it will keep the shape of an ice cream, this may help you feel very happy. What is Esky from the context？

A.a kind of food.

B.a case to preserve cold drinks or food.

C.electronic sky.

D.a refrigerator.