$1)$ Research suggests that option$-$pricing models that allow for the possibility of $\_\_\_\_\_\_\_\_\_\_$ provide more accurate pricing than does the basic Black$-$Scholes option$-$pricing model.

$1.$ early exercise

$2.$ changing expected returns of the stock

$3.$ time varying stock price volatility

A$)2$ and $3$ only

B$)1$ and $3$ only

C$)1,2,$ and $3$

D$)2$ only