He . documents by the time the boss came.

В данном предложении посмотрим на время, да и на само задание:

Скажем, что в данном случае нет отрицания и тут время Past Perfect!

Значит получаем такое предложение:

He  had prepared documents by the time the boss came.

mobile phones ,keeping fit

mobile phones entered our life not long ago, but today we can’t imagine our life without them. some doctors say that they are very harmful to the health, especially to the health of children.

the mobile phones emit electromagnetic radiation, and a number of different scientific institutes claim that this radiation is really very harmful, though still there is no hard evidence that showed that mobile phones caused harm in real humans. i try to talk over my mobile phone as less as possibleto avoid the health risks.

the british press. the british press consists of several kinds of newspapers. the national papers are the ones sold all over the country, with a large circulation, giving general news. there are two main types of national paper - the "popular" papers and the "quality" papers. the popular papers are smaller in size (they are tabloid size), with lots of pictures, big headlines and short articles. they are easy to read and often contain little real information. they give much space to opinions. they usually have "human interest" stories - stories about ordinary people and events. examples of this type of newspapers are "the daily mail". "the sun", etc. "quality" papers appeal to the more serious reader, who wants to read about politics and foreign affairs. these papers such as "the daily telegraph", "the guardian" are bigger in size (they are called "broad-sheets"), with longer articles and a wider coverage of events. they have different pages for home news, foreign affairs, features articles, fashion, business, sport and so on. people in britain buy more papers on sunday than on weekdays. the sunday papers have a higher circulation than the dailies. as with the dailies, there are both popular and quality sunday newspapers. the quality ones have different sections and a colour magazine (usually full of advertisements)