Answer $C$
Highest power can be calculated in the following way:
$$\Bigg\lfloor\frac{1000}{3}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^2}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^3}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^4}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^5}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^6}\Bigg\rfloor + \Bigg\lfloor\frac{1000}{3^7}\Bigg\rfloor = 333 + 111 + 37+12+4+1 + 0 = 498 $$
$\therefore C$ is the correct option.