According to the passage, which of the following can be found in areas with quite different climatic conditions on Earth

A．should add more useful features to their machines
B．often fail to make their products easy to use
C．should make their appliances as attractive as possible
D．often fail provide proper training in the use of their products

A．they can do so at a very Iow cost
B．they find their machines hard to operate
C．they have difficulty selling their products
D．they receive a lot of complaints about their machines