"""Extracts a multiple-choice answer from a prediction string.

This function processes a prediction string to extract a multiple-choice answer. It first removes any text following "Problem:" if present. Then, it replaces occurrences of "choice is" with "answer is" to standardize the format. Finally, it searches for a pattern matching "answer is" followed by a single letter (a, b, c, d, or e) in parentheses or without, and returns the matched letter in uppercase. If no match is found, it returns "placeholder".

Args:
    pred_str (str): The prediction string from which to extract the answer.

Returns:
    str: The extracted multiple-choice answer in uppercase, or "placeholder" if no valid answer is found.
"""