Впредложении нужно время определить, отрицательным сделать и вопросительным. i am writing from luxemburg.

Время present continous
отрицательное i'm not writing from Luxemburg
вопросительное Am i writing from Luxemburg?

I am writing from Luxembourg. - Present Continuous
Are you writing from Luxembourg?
I am writing from Luxembourg,aren't I?

1 V.Dal was sent by his parents to the Naval Cadet School.
2 Dal was taught medicine at Dorpat University.
3 While travelling about Russia,sayings and folk tales were collected by Dal.
4 Some Russian tales were written into poems by Pushkin.
5 Some of the stories were prepared for publication by Afanasyev.
6 Explanatory dictionary of the live great Russian language was published by Dal in the 19th century.
7 The year 2000 was declared the international year of vladimir dal by UNESCO.
8 A lot was done for the development of the Russian language and culture by Dal.

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ALTERNATING CURRENT

Alternating current (AC) is an electric current which periodically reverses

direction, in contrast to direct current (DC) which flows only in one direction.

Alternating current is the form in which electric power is delivered to businesses

and residences, and it is the form of electrical energy that consumers typically use

when they plug kitchen appliances, televisions and electric lamps into a wall

socket. A common source of DC power is a battery cell in a flashlight. The

abbreviations AC and DC are often used to mean simply alternating and direct, as

when they modify current or voltage.

Тhe number of cycles per second is the frequency of an alternating current.

Тhere are two frequencies: the standard for Europe is 50 cycles per second while

the standard for the USA is 60 cycles per second. А standard frequency has а great

advantage since different systems сan bе interconnected.

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