Which of the following is correct? a$.$ The time value of an at$-$the$-$money call option may be less than the time value of an in$-$the$-$money call option. b$.$ Because of the time value of money, the longer before an option expires, the less valuable the option will be$.$O c$.$ The time value of an in$-$the$-$money call option may be less than the time value of an out$-$of$-$the$-$money call option. d$.$ The time value of an at$-$the$-$money call option is always greater than zero.