下面两个英语填空,
1.The availability of oxygen is an essential--- for animal life,while carbon dioxide is
equally------ for plant life.
A.choice … optional B.duplication … selective
C.conversion … exchangeable D.condition … necessary
2.Old beliefs die hard:even when jobs became -----,the long-standing fear that
unemployment could return at a moment’s notice ------.
A.vacant … perished B.easier … changed
C.plentiful … persisted D.protected … subsided