The correct option is C Introducing a gene that makes them more sensitive to toxic substances
Toxicity of drugs on human can be studied by using transgenic animals by introducing a gene that makes them more sensitive to toxic substances. These transgenic animals are then exposed to the toxin and the effects and levels of their toxicity can be studied. Since these transgenic animals have a predisposition to be susceptible to a certain toxin, researchers can easily determine safe dosages by using these transgenic animals.