Commercial papers can be issued only by large and creditworthy companies because it is an unsecured debt.

Introduction:
Commercial papers are short-term debt instruments issued by companies to raise funds for their working capital requirements. They are typically issued for a period of 7 days to 1 year and are considered to be a cost-effective way of borrowing money. However, because commercial papers are unsecured debts, they can only be issued by large and creditworthy companies.

Explanation:
Unsecured Debt:
- Unsecured debt refers to a type of debt that is not backed by any collateral or specific assets of the borrower.
- In the case of commercial papers, there is no specific collateral attached to them. Therefore, in the event of default or bankruptcy of the issuing company, the holders of commercial papers do not have any specific assets to recover their investment.
- This makes commercial papers riskier than secured debts, which are backed by specific assets.

Creditworthiness and Size:
- Large and creditworthy companies have a higher ability to repay their debts and are considered less risky by investors.
- Creditworthiness is determined based on the company's financial stability, credit history, profitability, and ability to generate cash flows.
- Large companies generally have better access to financial resources and a strong track record, which enhances their creditworthiness.
- Due to their strong financial position and creditworthiness, large companies are more likely to attract investors and issue commercial papers.

Protection by the Government:
- Contrary to option 'A', commercial papers are not protected by the government.
- In case of default, the holders of commercial papers bear the risk of losing their investment.
- However, there are regulations and guidelines set by regulatory bodies, such as the Securities and Exchange Board of India (SEBI) in India, to protect the interests of investors and ensure transparency in the issuance and trading of commercial papers.

Conclusion:
Commercial papers are unsecured debts issued by large and creditworthy companies. They are not protected by the government and do not involve any collateral. The creditworthiness and financial stability of the issuing company play a crucial role in attracting investors and determining the interest rates for commercial papers.