题目

       Every living thing has genes. Genes carry information.   16   They make sure that humans give birth to humans and cows give birth to cows. They also make sure that a dog doesn’t give birth to a frog, or an elephant to a horse. However, genetic engineers take genes from one species-for example, a snake, and transfer them to another-for example, corn.   17   Such new life forms have been described, by some scientists as a real-life Frankenstein(科幻怪人).        Genetic engineers put duck genes into chicken to make the chickens bigger. They put hormones(We have __________ English class __________ Monday morning.A. an; in B. a; on C. a; in D. an; on