Research in plant biotechnology has focused primarily on characteristics that
a. improve resistance to pests, reduce the need for pesticides, and increase survival rates in adverse growing conditions.
b. allow genetically engineered seeds to be prepared within two months.
c. allow genetically engineered seeds to double in size within one year.
d. reduce the need for other genes to be introduced into a plant genome.

a. improve resistance to pests, reduce the need for pesticides, and increase survival rates in adverse growing conditions.

Plant biotechnology is a sub field of biotechnology which studies about the diversity of plant species and manipulates the genome of the plants in such a manner so as to make them resistant against the pests and diseases hence pesticides are not required, improving the yield of the crops, making the crops resistant against the adverse environment conditions like drought and thunderstorm.

On the basis of the above description, a. improve resistance to pests, reduce the need for pesticides, and increase survival rates in adverse growing conditions is the correct option.