It’s……since…… 用的时态主句从句的分开讲

since的四种用法 1) since +过去一个时间点 (如具体的年、月、日期、钟点、1980,last month,half past six).I have been here since 1989.2) since +一段时间+ agoI have been here since five months ago.3) since ...