Choose the best answer to complete each sentence 

Washing machines, vacuum cleaners, and dish washers are labor _______ devices which help us do housework easily and quickly.

Read the passage below and choose one correct answer for each question.

In the future, maybe all cars that run on petrol will be replaced by solar cars, which have been around for a while, but with recent developments in solar car design and the measurement of photovoltaic cells becoming smaller, the dream of a truly efficient solar car is more reality than fantasy. A solar car is a vehicle powered by photovoltaic cells, also called solar cells, which convert sunlight (light energy) into electrical energy. As a source of energy on earth, there is nothing like the sun: in a mere one thousandth of one second (.001) , the sun emits enough energy to fulfill our planet's energy needs for the next 5,000 years. It is a staggering fact, and an exciting one. Since the energy from the sun is responsible for renewable resources such as wind, tides, and heat, solar energy seems to offer the brightest future for not only cars, but for the entire energy crisis. Despite the appearance that solar energy may be the least, feasible among the current crop of alternative fuel propositions, new solar powered devices and more specifically solar powered cars are beginning to be developed. How do Solar Cars work?

The photovoltaic cells absorb photons from sunlight. This action generates heat, which the cells then convert into electrical energy and stores in an onboard battery. This process of conversion is called the photovoltaic effect. Not surprisingly, such a vehicle has zero emissions, and is very environmentally friendly. Unfortunately, at the moment photovoltaic cells are extremely inefficient, yet as time progresses the efficiency of these cells will grow. This will make solar energy and solar cars the fuel and car of the future - a closer reality.