Concept: Under Hindu marriage law, void and voidable marriages are different. A void marriage is invalid from the beginning, while a voidable marriage remains valid until annulled by court.
Step 1: Check Statement A.
A void marriage does not remain valid until decree. It is void from the beginning.
\[
A = \text{Incorrect}
\]
Step 2: Check Statement B.
A void marriage is never a valid marriage and no decree is necessary to make it void.
\[
B = \text{Correct}
\]
Step 3: Check Statement C.
A voidable marriage remains valid until it is annulled by a decree of the court.
\[
C = \text{Correct}
\]
Step 4: Check Statement D.
A voidable marriage is not invalid from the beginning. It is valid until annulled.
\[
D = \text{Incorrect}
\]
Therefore, the correct answer is B and C only.