<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_story_prefixes(label_type, label_dir=LABEL_DIR):
 """ Gets the Na text prefixes. """

    prefixes = [prefix for prefix in os.listdir(os.path.join(label_dir, "TEXT"))
                if prefix.endswith(".%s" % label_type)]
    prefixes = [os.path.splitext(os.path.join("TEXT", prefix))[0]
                for prefix in prefixes]
    return prefixes