def extract_course(transcript, i):
    """(str, int) -> str
        
    Return the nth course transcript record from the course transcript
    
    Precondition: i >= 1
    >>>extract_course('MAT,90,94,ENG,92,88,CHM,80,85', 1)
    'MAT,90,94'
    >>>extract_course('MAT,90,94,ENG,92,88,CHM,80,NE', 3)
    'CHM,80,NE'
    """
    return transcript[(i-1) * 10 :(i-1) * 10 + 9]