[] (often used as an adjective 常用作形容词) the act of choosing to be part of a system or an agreement决定加入；选择参与 () when the user of a company's website gives their email address so that they can be sent information about particular subjects, products or services选择性加入（公司网站的用户输入电子邮件地址即可得到有关主题、产品或服务方面的信息）