The manipulation of an organism's genes using modern DNA technology defines genetic engineering.
It is the process of making changes to the DNA of an organism in order to alter its characteristics or traits. This can be done to give them a better chance of survival, to select for desired traits for humans or for other specific purposes.
The other options are related but not a complete definition of genetic engineering.
Option 2 - the manipulation of an organism's genes to give them a better chance of survival - is a specific application of genetic engineering.
Option 3 - the selection of organisms for traits that make them more fit - is a natural process that can be artificially induced via genetic engineering.
Option 4 - the selection of organisms with desired traits for humans - is also a specific application of genetic engineering.