prolong vs pronounce slowly

prolong

verb
  • To lengthen in time; to extend the duration of 

  • To put off to a distant time; to postpone. 

  • To become longer; lengthen. 

  • To extend in space or length. 

pronounce slowly

How often have the words prolong and pronounce slowly occurred in a corpus of books? (source: Google Ngram Viewer )