21.  This thing consisted in various aspect of the society.First, the steady development of society is the main reason.

22.  The main reason is the development of their economy, thuse lead to the development of the medicine.

23.  At first, the economy of the developing country is the main reason.

24.  The main reason is the development in medicine and some other sciences and the development of the technology.

25.  The main reason is that these country of ecnormy has literally risen in the lastest years.

26.  I think there are main reasons as following: Firstly, when people want to finish their work as soon as they can, they always ignore some details of the work.

27.  I think these are not main reasons, in fact his most attracting feature is his noble spirit .

28.  There are two main reasons: firstly, the population of China becomes too large, and the government can not allocate everyone a job.

29.  According to scientists' saying , the main reason is temperature become warm and make water turning to vapour, going through a long distance and it will fall ..

30.  There have not flyovers or not enough flyovers , this is also a main reason why the traffic problem is so serious in Guangzhou.