THese are orange pencil cases (改为单数句）

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This is an orange pencil case.
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======以下答案可供参考======
供参考答案1:
this is orange pencil case
供参考答案2:
this is an orange pencil case.
供参考答案3:
this is/am oranges(橘子） pencil case
供参考答案4:
This is an orange pencil case.