Two analogies on manipulating items in a kitchen is given in the form "A : B. C : ?". The phrase "A : B" relates item A to its appropriate manipulation B. Your task is to replace the question mark (?) with the appropriate manipulation of item C, following the "A : B" relation. Your answer should be a verb which shows a way to manipulate the given object.
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Question: pump : pump. safe : ?

Answer: unlock


Question: jar : open. letter : ?

Answer: open


Question: backpack : unzip. walnut : ?

Answer:
shell