Answer: d. none of the above
Genetic engineering is a field of biotechnology which involves the manipulation of the genome of the organism so as to make it disease free, and suitable for human use by improving the quality of the organism.
Humans genetically engineer trees so as to make them resistant against the insects, for pharmaceutical production and to enhance their growth faster. Therefore, all these reasons supports the use of genetic engineering for trees, hence none of the above is the correct option.