Given the following declaration of an Oven class:

public class Oven $\{$

private int temperature;

$//$ EFFECTS: constructs an oven whose temperature is $65$F

public Oven$()\{$

$//$ stub

$\}$

$//$ REQUIRES: $180<=$ degrees $<=500$

$//$ MODIFIES: this

$//$ EFFECTS: heats oven to degrees Fahrenheit

public void preheatTo$($int degrees$)\{$

$//$ stub

$\}$

$\}$

Given the existing design of this class $($do not assume that there are any methods not explicitly included in the code presented above$),$ what would prevent us from designing tests for the preheatTo method?

$($a$)$

the modifies clause isn't specific enough

$($b$)$

there are no example calls to preheatTo that provides us with usage scenarios

$($c$)$

the temperature field is private and there is no accessor that will provide us with its value

$($d$)$

we don't know how the method is implemented

Select all possible options that apply.