private function getSelectedIndexChoices(array $answers) : array
    {
        $selectedChoices = [];

        foreach ($answers as $answer) {
            if (!ctype_digit($answer)) {
                throw new InvalidArgumentException('Answer is not an integer');
            }

            $answer = (int)$answer;

            if ($answer < 1 || $answer > count($this->choices)) {
                throw new InvalidArgumentException('Choice must be between 1 and ' . count($this->choices));
            }

            // Answers are 1-indexed
            $selectedChoices[] = $this->choices[$answer - 1];
        }

        return $selectedChoices;
    }