4. The researchers in our labs * to invent a cheap alternative to sugar, but their efforts did not succeed a developed b. attempted C. informed d. warned 5. Emission of chemicals can serious environmental damage. a invent b. make C. Cause d. persist 6. The task instructions are very a I cannot understand them. a complex b. alternative C. positive 7. After the storm, a thick layer of dust on the floor and furniture. a. caused b. made c. assembled d. accumulated 8. In his recent article, Dr Brown several reasons why the COVID-19 can spread quickly. a. objected b. aimed C. cited d. insisted