Which is the correct option to complete the text below?

Chock-a-block

Today, this adjective means 'crammed full with people or things' (the narrow roads are chock-a-block wilh vehicles).

Chock derives chock-full, a Middle English word unknown origin meaning 'very full'. It rhymes nicely the block in question, more fully known as a pulley block, part a block and tackle. This is a device much used boats and elsewhere to make lifting heavy weights less demanding.

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