Genetic Engineering is possible because 

The correct answer is Restriction endonucleases purified from bacteria can be used in vitro. 

 Key Points

• Recombinant DNA is used to make changes to the original genome of a plant or animal to add desired traits that are not present in them naturally and to delete genes that are harmful to plants and animals.
• This process is known as genetic engineering.
• The presence of restriction endonuclease, which enables us to alter the original DNA sequence, makes genetic engineering conceivable.
• As restriction enzymes, restriction endonucleases can recognise and cut DNA only at specific locations known as restriction sites.

Therefore, the correct answer is restriction endonucleases purified from bacteria can be used in vitro.