Time and again in the passage, the author has discussed about the downsides of bitcoins. However, opening two sentences of the 2nd para, opening sentence of the 3rd para and the 5th sentence of the last para, all point to the fact that people are indeed buying bitcoins, and the only reason that could define this action is the appreciation in the value. Hence, D will be the best answer here. E cannot be the correct answer because option C talks about "laws in countries" but the passage includes nothing as such.