Why isen’t it C? I mean if the value of the underlying decreases the put option should increase right or?
without dividends and if you assume the Black-Scholes model, the price of a European put is
P=\frac{X e^{-r(T-t)}}{2}\textrm{erfc}\left[\frac{\ln\frac{S}{X}+(r-\frac{\sigma^2}{2})(T-t)}{\sqrt{2\sigma^{2}(T-t)}}\right]-\frac{S}{2}\textrm{erfc}\left[\frac{\ln\frac{S}{X}+(r+\frac{\sigma^2}{2})(T-t)}{\sqrt{2\sigma^{2}(T-t)}}\right]
As you say, as the underlying S decreases, the put option increases in value.
I don’t like the way this problem is worded.
They’re using directly related' to mean that the price of the put increases as the underlying increases and inversely related’ to mean that the price of the put decreases as the underlying increases, and vice versa
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Yeah I got a bit confused but it feels like they are using tricky language sometimes to confuse the student. Thanks for agreeing with me 
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