9Cecile M, Xavier S, Montserrat G(2009). Risk perception as a function of risk exposure amongst rock climbers[ J ]. Psychology of Sport and Exercise, 10 (7), 193-200.
10David R B (2004). Influence of hygiene on gastrointestinal illness among wilderness backpackers[ J]. Journal of Travel Medicine, 11 ( 11 ) ,27-33.
