With answers Изд. 2-е Essential Grammar in Use: A self-study reference and practice book for elementary students of English:

Now they all form a new illegal residency. The new illegals never mix and never enter into contact with the old ones who have been working in the country for a long time. This plainly makes life more secure for both parties. The formation of new illegal residencies where there were already old ones in action is yet another example of the constant striving for duplication. However important the problems of recruiting agents, training them and organising agent networks may be, there is still one overriding objective: the acquisition of secrets belonging to an enemy or a probable enemy. The material acquired by the GRU breaks down into information, documents and specimens or samples. Information includes commentaries and reports. Documents are not the subjective opinions or observations of agents but official secret papers, books, drawings or copies of them. Specimens or samples are self-explanatory: actual weapons, examples of military technology, instruments and equipment which the GRU uses for study and copying ...»