**Core Concept**
Restriction endonucleases are enzymes that cleave DNA at specific recognition sites, resulting in fragments that can be separated and analyzed. This process is a crucial step in molecular biology and genetic engineering.

**Why the Correct Answer is Right**
The DNA fragments formed by restriction endonucleases are separated by gel electrophoresis, which is a laboratory technique used to separate DNA molecules based on their size. As the negatively charged DNA fragments migrate through a gel matrix, they are pulled towards the positively charged electrode, with larger fragments moving more slowly and smaller fragments moving more quickly. This allows researchers to visualize the separated fragments using a technique called Southern blotting or by staining the gel with ethidium bromide.

**Why Each Wrong Option is Incorrect**
**Option A:** PCR (Polymerase Chain Reaction) is a method used to amplify specific DNA sequences, not separate DNA fragments.
**Option B:** DNA sequencing is a technique used to determine the order of nucleotides in a DNA molecule, but it is not used to separate DNA fragments.
**Option C:** DNA cloning is a method used to create multiple copies of a DNA molecule, but it is not used to separate DNA fragments.

**Clinical Pearl / High-Yield Fact**
To remember the order of DNA separation techniques, use the mnemonic "GEL" - Gel Electrophoresis, then Label (Southern blotting), and finally Elute (to extract the separated DNA fragments).

**Correct Answer: A. Gel electrophoresis.**