The correct answer is: A. Redeemable Equity shares.

Equity shares are the most basic form of ownership in a company. They represent a share of the company's assets and profits. Equity shares cannot be redeemed by the company, unless all other shareholders agree. This is because equity shares represent a permanent interest in the company.

Preference shares are a type of equity share that has a higher claim on the company's assets and profits than ordinary shares. Preference shares can be redeemed by the company, but only if the terms of the issue allow for this.

Debentures are a type of loan that a company can issue. Debentures are usually secured against the company's assets, and they must be repaid with interest. Debentures can be redeemed by the company, but only if the terms of the issue allow for this.

Fully convertible debentures are a type of debenture that can be converted into equity shares at a certain point in time. Fully convertible debentures are usually issued when a company needs to raise money but does not want to dilute the ownership of its existing shareholders.

In conclusion, a company cannot issue redeemable equity shares. This is because equity shares represent a permanent interest in the company.