missing operating system是操作系統丟失的意思。
重點詞匯解析：
missing 基本詞匯
英 ['m?s?]? 美 ['m?s?]
adj. 失蹤的；失去的；漏掉的
動詞miss的現在分詞形式.
Police are combing the woods for the missing children.
警察搜遍樹林以尋找失蹤的孩子。
missing from 從…失掉〔掉隊〕的?
missing in action 戰鬥中失蹤
詞匯的同近義詞
absent 核心詞匯
英 ['?bs?nt]? 美 ['?bs?nt]
adj. 缺席的；不在的；缺乏的
vt. 使缺席
Many students were absent, notably the monitor.
許多學生缺席，特別是連班長也沒來。
Why did you absent yourself from school yesterday?
昨天妳為何不到校?