题目

    Almost everybody in America will spend a part of his or her life behind a shopping cart. They will in a lifetime, push the chrome­plated_contraptions many miles. But few will know—or even think to ask—who it was that invented them. Sylvan N. Goldman invented the shopping cart in 1937. At that time he was in the supermarket business. Every day he would see shoppers lugging groceries around in baskets they had to carry. One day Goldman suddenly had the idea of putting baskets on wheels. The wheeled baskets would make shopping much easier for his customers, and would help to a一只杂合的黑毛家兔产生200万个精子，这些精子中含隐性基因（白色基因）的约有A.25万B.50万C.100万D.200万