PRESENT SIMPLE/SIMPLE FUTURE If you_(want) to travel long distances on
your bicycle, you must learn how to mend a puncture. As soon as your
tyre_(become) flat, get off the bike
or you will_(damage) the wheel. Then turn
the bicycle upside down. Once it_(be) in
position, remove the tyre using levers or, if you_(have) nothing else, use spoons. When the
tyre_(be) off, pump up the inner tube. Put it in some
water and turn it until you
_(see) bubbles coming
from it. This your puncture. Before you_(apply)
the patch, you must clean and dry the area around the hole. After_(put) glue around the hole and wait
until it_(dry) a little. Then select a suitably
sized patch. Stick the patch over the hole and don't forget to put
some chalk over it. Unless you do this the inner tube_(stick) to the inside of the tyre. Replace the
tube, pump up the tyre and ride away. I_(not/know) if
you_(be able to remember
all this, but it's worth trying because you never know when it_(be) useful to you.
this you.
The center of this world is a tiny silicon plate of a few square millimeters, an integrated circuit, or a chip, as it is more commonly known. The integrated circuit is undoubtedly one of the most sophisticated inventions of man, science and technology. As the operation os an integrated circuit depends on microscopic "components", the purity of all materials and the cleanness at the plant they are produced at must be of the highest quality.
In the past it took scientists and reserchers a whole lifetime to make a few thousand calculations, whereas for a modern computer this task is a matter of a few seconds. At present computers capable of performing billions of operations a second are required. In the next few years engineers will complete the work on computers of above 2 billion operations a second. It will take a few more years to produce a 10-billion operationscomputer. According to some researchers, we are close to what can be regarded as a true physical limit. But other specialists think that photons will make the operation a thousand times faster. This means that in the future it will be possible to expect the appearance of photon computers and that computations will be done by means of light. In a few decades a new age of light may replace the stil youthful electronic age. The race is going on.
2. The Trans-Siberian Railway is divided into six railways in Ural, Siberia and the Far East, didn`t it?
3. George Pullman became well known for luxury sleeping cars called Pullman cars in his honour, didn`t he?
4. These express trains will proceed to the final destination without any stops, won`t they?
5. Both direct and alternating current can be used on electrified railways, can`t they?
6. Powerful track-laying machines have been developed for the building of railroads, haven`t they?