How would you edit the following sentence from Grace's original letter to fit the conventions of standard grammar and usage? (37)

"I have got a little baby sister she is nine weeks old and is just as cunning as can
be."

A. "I have got a little baby sister, she is nine weeks old and is just as cunning
as can be."

B. "I have got a little baby sister; She is nine weeks old and is just as cunning
as can be."

C. "I have got a little baby sister, she is nine weeks old and is just as cunning
as can be."

D. “I have a little baby sister: she is nine weeks old and is just as cunning as can be.