从Selectbox删除所有选项，除了第一个和选中的。

I have a html select box with several options. Upon selection of an option I want Only the selected option and the first option to be shown in the select option dropdown. I know how to filter and show only one option but I cannot figure out how to include both option where the 'selected' option remains 'selected'. I have include snippets similar to of my code as well as a demo.I have a html select box with several options.