Depends on what the question refers to:
The longest "running" event is the Marathon, but the longest event in terms of distance in the athletics is the Mens 50 kilometre walk (but you certainly aren't allowed to run in that).
Alternatively there are a whole series of events that have been included in every Olympics, therefore there is no single longest running event in terms of being at every Olympics.
How many 3s in 313433535333?
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How many fifths are in 6 tenths?
What is half of 74?
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The more you take the more you leave behind what am I?
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Ano ang kahulugan ng iskolarling pagpapahayag?
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Ano ang papel na ginagampanan ng mga impormasyong ito sa mapa o sa globo?
Which of the following statements is true about storing classified documents?
When two pieces of cui or other unclassified information are posted online together?
What are the solutions to the crazy kiwi game?