解析过程：
settle down是动词词组
settlement是名词
规律方法：
settle down在句中一般要作谓语,如：They settled down in the USA in 1980.
settlement 表示定居或者定居者的意思
In the early days of the settlement of Australia, enterprising settlers unwisely introduced the European rabbit.
澳洲殖民初期,具有冒险精神的殖民者轻率地引进了欧洲兔子.如果还有其他疑问,可以去“状元365”提问.