You observe that the price of a stock decreases significantly, and at the same time the price of a put option on this stock also decreases.

a. This cannot happen, since the lower the stock price, the higher the put value.

b. The risk-free rate must have decreased significantly.

c. This may be due to the sudden decrease in investors' perceived future volatility.

d. This may be due to the sudden decrease in the hedge ratio.

e. Two of the above are correct.