SBR Q28 AVCO – Financial Instrument Help please

I have read the answer for this question and i still do not understand why Lidan is classed as liability and not an equity. Could someone please explain.

Lidan has in issue two classes of shares: A shares and B shares. A shares are correctly classified as equity. Two million B shares of nominal value of $1 each are in issue. The B shares are redeemable in two years’ time at the option of Lidan. Lidan has a choice as to the method of redemption of the B shares. It may either redeem the B shares for cash at their nominal value or it may issue one million A shares in settlement. A shares are currently valued at $10 per share. The lowest price for Lidan’s A shares since its formation has been $5 per share.