She promised that she would do ________ catch up with others.A.all what she could doB.all she could toC.what she could doD.all she could
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B解析to catch作目的状语to不能省略；what不能引导定语从句，故可以排除A、C、D．all she could to＝what she could(do)或all that she could(do)to．