1. Complete the sentences with still, yet, already or just. 1 We have just booked our holiday and turned off the computer.
2 We’ve packed our suitcases even though we leave next week.
3 Have found your passport ? The taxi is outside.
4 I haven’t finished my homework and I have to hand it in tomorrow.
5 Mark hasn’t arrived and dinner is ready.
6 Barbara has been skiing in Austria. She returned yesterday.

Areas with no source of electricity remain in darkness until the
comes up, because street lights need a power supply. British firms offer new appliances, such as solar-powered street lights. They work by using energy accumulated during the day from a solar panel. The batteries are being charged during the day and then it's power is used for lighting. The system can be used for one individual light or a number of them. In the south of Saudi Arabia a motorway tunnel miles from any power supply is lit day and night by solar-powered devices. The advantages of sun-powered lamps are
that they can bring light to areas distant from any other power supply and that they do not pollute the environment.

The Sun is an effective source of energy for distant areas with undeveloped infrastructure. Solar energy can be used for charging batteries during the day. Some  cities use the solar-powered street lights in motoway tunnels that are far away from the usual power plant.The solar power is unlimited and doesn't pollute  the environment . Nonetheless, using the batteries as a storage for energy  is quite expensive. That's why it's still important to develope the solar energy transforming as a form of power for infrastructures.