Final answer:
Proposed regulations cannot become final until at least 30 days after they are published in proposed form, and the public must be given an opportunity to comment on them before they become final.
Step-by-step explanation:
The correct statement regarding Proposed Regulations is option (d): Only (a) and (c) are correct.
Option (a) is correct because proposed regulations cannot become final until at least 30 days after they are published in proposed form. This allows for public input and review.
Option (c) is correct because the public must be given an opportunity to comment on Proposed Regulations before they become final. This ensures transparency and accountability in the rule-making process.