11.................. are you doing? - I’m reading a book. A. WhomB. WhoC. WhoseD. What 12. ................. coffee is this? – It’s mine. A. WhoB. WhichC. WhoseD. What 13. ................. of these problems are you most interested in? A. WhoB. WhomC. WhichD. What 14. ................. do you know about this subject, and who taught it to you? A. WhichB. WhoC. WhatD. Whom 15. ................. is responsible for the accident? A. WhoseB. WhoC. WhichD. Whom 16. ................. can be an excellent source of free, renewable energy for poor farmers. A. TurbineB. BiogasC. Solar panelD. Bulb 17. The government has warned that Britain will face power ................. in the coming winters. A. coalB. shortagesC. slogansD. energy 18. Wind power is one of the earliest ................. sources of energy used by humankind. A. alternativeB. pollutedC. harmfulD. exhausted 19. Nobody can predict exactly when supplies of fossil fuels will be ................. However, we all know they quickly reduce in quantity. A. installedB. pollutedC. harmfulD. exhausted 20.Biogas can be used to ................. natural gas in cooking, heating, or electrical generation. A. use upB. replaceC. polluteD. install