* Restriction enzymes are biological scissors that recognize and cut specific DNA sequences. They are essential tools in molecular biology and genetic engineering for manipulating DNA.

Let's look at the other options:

* Ligases are enzymes that join DNA fragments together. They are the opposite of restriction enzymes.

* Polymerases are enzymes that create new DNA strands using a template. They are involved in DNA replication and repair.

* Helicase is an enzyme that unwinds the double helix structure of DNA, making it accessible for other enzymes.

In summary: Only restriction enzymes are specifically designed to cut DNA, making them the correct choice for studying DNA.