Which of the following statement is not true?

a$.$ Volatility smile is a plot of implied volatility versus exercise pfice.

b$.$ Implied volatility is the volatility value that makes the price determined by the Black$-$Scholes formula equal to the current market price.

c$.$ A derivative is a financial instrument whose value is derived from the value of some underlying asset.

d$.$ A call option gives one the right to sell some underlying asset at an exercise price.

e$.$ A put option is a derivative.