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: This should be secured in the stern-sheets of the first boat.

Answer: This

Question: This process is called 'laying' and is always carried out in the opposite direction to that used in the previous stage of twisting the strands; it is, moreover, distinct from the simple spin or twist and is twofold, in that:

Answer: This process

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