def find_best_match(long_seq, short_seq):
    """
    Using indexing to extract DNA sequence section by section, finding the best matched.
    :param long_seq: str, the given DNA sequence to be matched.
    :param short_seq: str, the given DNA sequence to match.
    :return: str, the best matched of DNA section.
    """
    best_match_score = 0
    best_match_index = 0
    for i in range(len(long_seq) - len(short_seq) + 1):
        match_score = 0
        for j in range(len(short_seq)):
            if long_seq[i+j] == short_seq[j]:
                match_score += 1
        if match_score > best_match_score:
            best_match_score = match_score
            best_match_index = i
    return long_seq[best_match_index:best_match_index + len(short_seq)]