Insulin Derived from Animals Was Used to Treat Diabetes Cases

Insulin derived from animals was used to treat diabetes cases until genetic modification techniques arose in the late 1970s.Which of the following was a drawback of nonhuman insulin?

A) Impurities in the insulin led to allergic reactions in some human patients
B) Animal-derived insulin carried other diseases
C) Animal insulin was expensive to obtain
D) Small chemical differences between animal and human insulin led to allergic reactions in some human patients