YOU SAID:
is this a pencil that is mine?
INTO JAPANESE
これは私は、鉛筆ですか。
BACK INTO ENGLISH
Is this me a pencil?
INTO JAPANESE
この私は、鉛筆ですか。
BACK INTO ENGLISH
This is my pencil?
INTO JAPANESE
これは私の鉛筆ですか。
BACK INTO ENGLISH
This is my pencil?
That didn't even make that much sense in English.