    Senfence 1: He’..’ said’ there -’ were  complex: réasons . for’ the “increased  ttumbers' “of -cases “and scientists | were  only just beginning to understand the  tisk factors .    Sentence. 2: However . he said’. The  reasons. behind the-- increase: - in  incidence -are’ more complex and were  just beginning ‘to: understand the risk  factors . .