7 He has to go out since his boss called him.
`->` Giải thích : since + clause =because + clause : vì
8 He was so seriously ill that he has to finish his work.
`->` Cấu trúc : so..that (quá...đến nỗi mà….) :
`->` S + be /V + so + adj/adv + that + S + V