“…What strategies should be introduced to tackle this problem? Although some authors have discussed the reasons and given some suggestions on this problem after experiments [LAWRENCE & AL., 2001;RUMSEY, 2002;SPINELLIS, 2003;CASSERLY & BIRD, 2003;DELLAVALLE & AL., 2003;DIMITROVA & BUGEJA, 2006;WREN & AL, 2006;, deep and systematic analyses still need to be conducted.…”