Объясните, какое значение всему предложению выделенные формы глагола, и переведите предложения на язык. although machine-building has been a branch of human activity for centuries, only in the 20th century have machines begun to assume such an all-important role. 2. the engineer had visited many plants and designing offices, he had personally examined a great deal of different types of machines and had done a lot of work on his thesis, before performing a large number of experiments. 3. i’d like to know whether the series of experiments i have already performed and the data which i have obtained are enough. 4. these remarkable technological achievements have become possible by specially designed mechanisms and machines. 5. man has obtained ultrahigh and ultralow temperatures, ultrahigh vacuums, superhigh pressures, ultrahigh strength, superelastic and superconducting materials and has been able to study the interaction of superhigh-energy particles.