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The katakana form's ジ sound comes from two bases: from "sh," as in "sheep" AND from the "ch" sound in "cheese." When I am asked to identify the character, during study, that is producing the ジ sound, I never know which answer is correct or why. Is there some kind of rule for making the distinction? Thank you.
How do I know, for Katakana, whether it is シ plus ダクテン or チ plus ダクテン which is forming the ジ sound?