选自Lesson23Anewhouse新居Ihadaletterfrommysisteryesterday.ShelivesinNigeria.Inherletter,shesaidthatshewouldcometoEnglandnextyear.Ifshecomes,shewillgetasurprise.Wearenowlivinginabeautifulnewhouseinthecoun

　　选自

　　Lesson23Anewhouse新居

　　Ihadaletterfrommysisteryesterday.ShelivesinNigeria.Inherletter,shesaidthatshewouldcometoEnglandnextyear.Ifshecomes,shewillgetasurprise.Wearenowlivinginabeautifulnewhouseinthecountry.Workonithadbegunbeforemysisterleft.Thehousewascompletedfivemonthsago.Inmyletter,Itoldherthatshecouldstaywithus.Thehousehasmanylargeroomsandthereisalovelygarden.Itisaverymodernhouse,soitlooksstrangetosomepeople.Itmustbetheonlymodernhouseinthedistrict.

　　请分析Inmyletter,Itoldherthatshecouldstaywithus.（还有为何用could）

　　请详细分析（不是翻译），从时态，结构，that，could分析