单项选择题

Most churches have Christmas Eve services. The services usually begin just before midnight on Christmas Eve and end early Christmas morning. It was not until the 4th century that the church in Rome began to celebrate Christmas. Midwinter festivals had always been celebrated by many peoples. The approach of the winter time, as the days grew shorter and colder and the sun seemed to threaten to disappear entirely, was time of fear. But the shortest day also meant that winter was leaving and that ahead were spring, the warmth of the sun and the return of vegetation (植被) of the fields.
The day before the vacation begins, schools have Christmas parties and prograrms. The children sing Christmas songs and recite Christmas poems. They trim their Christmas trees with strings of colored lights. They put glass ornaments on the trees. They throw little pieces of white paper over the trees and put white paper or a white sheet around the feet of the trees, so that they seem to be covered with snow. ,Sometimes they hang Christmas cookies and little candies around them. Little children hang up their stockings on Christmas Eve near their beds. and they believe that when they are asleep, Santa Claus will come to visit them and put presents into the stockings.
The underlined word "trim" in the second paragraph means ______ .
A) pull B) decorate C) burn D) paint