Once. According to Zhihu, the American "Major League" thinking exploration and research activity is a mathematical thinking exploration and research activity with outstanding influence in primary and secondary schools in the United States and North America, and it is also a mathematical thinking exploration and research activity with global influence. Held once a year, it is divided into three stages: the first stage, the second stage and the research carnival. The activity questions in the first stage enable students to understand and appreciate mathematics, stimulate students' innovative spirit, stimulate students' interest in learning mathematics and cultivate students' spirit of active exploration. The activities in the second stage cultivate students' creative thinking, critical thinking and practical problem-solving ability. The carnival is very challenging, focusing on cultivating students' creative problem-solving and innovative thinking ability.