题目

In the U.S. Mother’s Day is a holiday celebrated on second Sunday in May. It is a day when children honor their mothers with cards,gifts and flowers. First observance in Philadelphia in 1907,it is based on suggestions by Julia Ward Howe in 1872 and by Anna Jarvis in 1907. Although it wasn’t celebrated in the U.S. until 1907,there were days honoring mothers even in the days of ancient Greece. In those days,however,it was Rhea,the Mother of the gods that was given honor. Later,in the 1600’s,in England there was an annual celebration called “Mothering Sunday.” It was celebrated dur若等腰三角形的顶角为30°，那么这个等腰三角形的底角为_____°