9Berry R J, Li Z, Erickson JD, et al. Prevention of neural-tube defects with folic acid in China. [J]. The New Eng J Med , 1999, 341 : 1485-1491.
10Nigel B, Rogelio P P, Rachel A. Indoor air pollution in developing countries: A major environmental and public health challenge [ J]. Bulletin of the World Health Organization , 2000, 78 ( 9 ) : 1078.
