Quetions about Energy

Could anyone help me with this passage about “Energy”? I find this one interesting. However, I find some questions confusing.

“…For many people living in rural areas in developing countries of the world, biogas is the largest energy resources available and costs almost nothing. The main use of biogas is for cooking and heating. As biogas is smoke-free, it helps solve the problem of indoor air pollution. Moreover, plants waste and animal manure cost almost nothing….”

1. People in rural areas shouldn’t use biogas because it is_______________.

A. unavailable B. expensive C. harmful D. cheap

1. The only disadvantage of using biogas is that it is_______________.

A. smoke-free B. clean to environment C. costly D. available

Question 1: I think there may be a typo mistake here: It should be “People in rural area should use…

and the answer should be “D. cheap”

Question 2: The expected answer is “C. costly”. I quite disagree with this statement because “costly” means “expensive”. However, I can’t find the most suitable answer here because the rest A, B & D are out of questions. I think we should modify this question a little bit but I am not be able to do it.

Thank you for spending time reading my questions.