“My sister's birthday is in Decetember.”的同义句

“My sister's birthday is in Decetember.”的同义句

My sister's date of birth is in December.=
My sister was born in December.

My sister was born in december

前面改成l'm

it's in December when（that） my sister's birthday is celebrated。
it is -----that----是强调句型，用在这里强调的是你妹妹生日的时间。这里用when也可以。
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