is this your case 语法错误吗?

is this your case 语法错误吗? Is this your pencil case中文 is this your case,is this case yous这两种语法有没有错误 is this a pen ___ your pencil case Exuse me!Is this your pencil case?改为复数形式 me,escuse,is,this,case,your,连词成句 This is a new pen.( ) it in your pencil case This is your case.变复数…… Is this your watch in the lost and found case?怎么翻译?特别是case Ok,and this is my book and this is your pencil case ,Jane. whose is this red case This is his pencil case.