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In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

If the system had pulleys, it would still need what to operate?, Context: The tide-predicting machine invented by Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.
Output:
wires