In this task, you are given a sentence. You must find the primary subject in the supplied sentence. The output must be a sub-sequence in the sentence.
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Question: Next, a certain number of yarns are twisted together to form strands which, at the Admiralty Ropery, Chatham, are usually 150 fathoms in length when completed.

Answer: a certain number of yarns


Question: When new and untreated it is deep golden-brown in colour.

Answer: it


Question: The ribbons are then twisted up into yarns, and the twist given binds the fibres firmly together so that they hold by friction when the yarn is subjected to strain.

Answer:
The ribbons