问题如下：
Which of the following equity securities that an investor consider the least risky?
选项：
A.Putable preference shares.
B.Callable preference shares.
C.Non-callable preference shares.
解释：
A is correct.
Putable shares, whether common or preferred, can be sold back to the issuer at a predetermined price.
The predetermined price creates a floor for share prices, reducing uncertainty about future cash flows for investors.
老师好，可以再详细解答一下吗？谢谢
