Kate's father took her to the hospital to see her one-day-old baby brother. They drove there straight from school. Kate had never been inside a hospital before.  ①This was a new experience for her.

    At the gate there was a large sign listing all the departments of the hospital, with arrows (箭头) showing how to find them. When Kate saw the A&E department(急救室), she asked,“What do those letters stand for?”“Accident and emergency,” replied her father,

②“Last spring, I took our sister there because she fell off her bike,”

读图，回答下列问题．

形成南方地区与北方地区自然环境差异的主要因素是（     ）