According to the British Daily Mail, scientists and psychologists have long-unsolved a mystery-why do we forget what happened in childhood? This is the most carefree and happiest time in life. At present, two scientists believe they have solved the mystery. They pointed out that the rapid growth of cells in the brain's memory center at the beginning of life means that the brain memory cells that existed early The key links between them will be replaced by new ones, so people's childhood memories are unlikely to be restored. They believe that this can explain why humans have very few memories of childhood. In fact, it is impossible to recall childhood life. The details also have certain benefits, it can make people not often remember some unpleasant events that happened during the infancy. According to this passage, the main reasons for missing childhood memories are? ['The rapid development of brain memory cells.', 'Memory fades over time.', 'Low language skills early in life.', 'Children have self-protection mechanisms.']