Create a function that takes a string as the first argument, and a (string) specification as a second argument. If the specification is "word", return a string with each word reversed while maintaining their original order. If the specification is "sentence", reverse the order of the words in the string, while keeping the words intact.
str = "There's never enough time to do all the nothing you want"
flip("Hello", "word") ➞ "olleH"
flip("Hello", "sentence") ➞ "Hello"
flip(str, "word") ➞ "s'erehT reven hguone emit ot od lla eht gnihton uoy tnaw"
flip(str, "sentence") ➞ "want you nothing the all do to time enough never There's"
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