giúp mk vs ! 15. .., methane can be used as fuel. A. It is produced by the fermentation of organic matter. B. Produced by the fermentation of organic matter. C. The production by the fermentation of organic matter. D. The fermentation of organic matter. 16. ..to the unaided eyes, ultraviolet light can be detected in a number of ways. A. Although is invisible B. Despite invisible C. Even though it invisible D. Although invisible 17. ....people with high blood pressure may not exhibit symptoms, they may not be aware they have the disease. A. Because B. Although C. However D. So that 18. Although.a country illegally is risky, the alien who finds work may believe the risk worthwhile. A. when entering B. he enters C. entering D. having entered 19. She failed the test..she studied hard. A. although B. even though C. as D.A or B 20. the fact that she failed the exam, she did not look disappointed. A. Although B. Despite C. In spite of D. B or C 21. ..sighting an approaching car, some drivers tend to speed up. A. When slowing down instead of B. Instead of slowing down at C. When instead of slowing down D. Instead of slowing down when