import string
import random


def random_string(number, length, num_letters):
    """
    Generate a list of random strings of lower case letters.
    """
    result = []
    letters = string.ascii_letters[:num_letters]

    for i in range(number):
        word = []
        for j in range(length):
            word.append(random.choice(letters))
        result.append(''.join(word))

    return result