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22 V. Choose the correct answer. 1. Scientists … these plants for antimicrobial activity for some years. a) investigates c) have been investigating b) is investigating d) has investigated 2. He … an interesting talk with his foreign colleague. a) has been c) have had b) is having d) have 3. We … this doctor for many years. a) know c) knows b) have known d) have been knowing 4. She … her first paper in an international journal recently. a) has published c) publishes b) have published d) is publishing 5. The doctor … this technique for several years. a) use c) has been using b) is using d) uses 6. The physician … the patient’s blood pressure now. a) is taking c) takes b) take d) has taken 7. If the patient … a strict bed regimen, he will be well again soon. a) will follow c) is following b) has followed d) follows 8. So far, scientists … a gene for ageing. a) is not finding c) have not found b) do not find d) has not found 9. Vitamins … biomolecules that act as catalysts in chemical reactions. a) has been c) is b) are d) have been 10. In spite of numerous studies the mechanisms of atherogenesis … uncertain. a) remain c) remains b) is remaining d) has remained