         Sentence “17 What. ‘has’ caused -savania  regions. to grow. into. the. South American.  trapies:.in the’ last 34 niillion. years?    Sentence: 2? Climate. Fluctuations. during  the! last: 34 ‘million. years. have ‘allowed.  savanria i region&: to’ “expand "into. the.  tropics.         