Transgenic animals are used

The correct option is D All of these
Animals with their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals.

Many transgenic animals are being developed to help us understand how genes contribute to the development of diseases. The purpose of the transgenic animals is to serve as models for human diseases so that investigation of new treatments for those diseases is possible. Today, transgenic models exist for many human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's disease.

The synthesis of the biological products that are required to treat certain human diseases is expensive. As a solution, transgenic animals can be made to produce useful pharmaceutical products. This is done by introducing genes which code for a particular product in a transgenic model animal. Medicines for emphysema have been obtained from the transgenic animals.

The safety and efficacy of vaccines are tested before their administration into the human masses. This is done by administering them into certain genetically modified animals. One such example is the use of transgenic mice for testing the safety and efficacy of the polio vaccine.