Option C and D
My dog is beautiful; her eyes are her best features is correct because the semi colon show details of the connection between the independent clauses and it shows that “the dog is beautiful” is supported by the other clause, “her eyes are the best feature”.
Option D is also correct because a period can be used to show the connection between the two clauses. Option A is not correct because it is not punctuated and the clauses have to be linked by punctuation.
Option B is also wrong because a comma does not show a strong connection between the independent clauses. It can only be used in a continuing sentence not to link independent clauses