The horseshoe crab breathes by means of its

Book lungs

Explanation:

The horse shoe crab has a hard outer surface carapace which has the shape of a horse shoe.

It has book lungs which come in 5 sets. The lungs are usually found on the ventral side of the crab.

The book lungs acts as gills which is used in breathing when the horseshoe crab is in water . The book lungs also helps the crab to breathe on land for a certain period of time provided the lungs are moist.

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c.) polymerase chain reaction

- "unlike the original dna fingerprinting method, dna profiling does not use restriction enzymes to cut the dna. instead it uses the polymerase chain reaction (pcr)? to produce many copies of specific str sequences. pcr is an automated procedure that generates lots of copies of a specific sequence of dna."