4.C【解析】主旨大意题。根据文章第一段可知现在MIB课程越来越受欢迎。本段最后一句There are valid reasons for so much popularity of MIB course.提出了这一课程受欢迎有很多原因，文章接下来三段就对具 体的原因进行了说明。故C项正确。

　　May Day, the first day of May, is celebrated as a spring festival in many countries. It marks the approach of summer.

　　The English developed their May Day festival from the Roman festival called Floralia. In the festival of Floralia, the Romans gathered flowers to honor the goddess of spring, Flora. In the Middle Ages, May Day became the favorite holiday of many English villages. People gathered flowers to decorate their homes and churches, sang spring songs and chose a king and a queen of May. Villagers danced around a tall pole fixed upright in the ground, called a maypole, each holding the end of a ribbon attached to the top of the pole. They tied the ribbons around the pole until it was covered with bright colors. They collected dew(露水)on May Day morning and washed their faces with it because they believed that the dew on the day had the magic power to regain youth.

Nowadays in Britain people no longer attach great importance to the day, but in some towns and villages people still celebrate it by choosing the May Queen and dancing around the maypole. May Queen is a girl selected as the most beautiful girl on May Day. She is usually crowned with flowers and often driven in procession through the street. In the United States, the day has never been celebrated with the same enthusiasm as in Britain. But in many American towns and cities,