I'm trying to make a mad libs program and am having trouble with `.replace` and don't know why its not working, I'm pretty new to coding and don't know too much.

```
import random

def main():
    libs = input('Hello! Would you like to play MadLibs? Enter y or n: ')
    libs = libs.lower()

    while libs == 'y':
        paragraph = madLibs()
        para = replace(paragraph)
        print(para)
        libs = input('Would you like to play again? ')
        libs = libs.lower()

    if libs == 'n':
            exit()

    if libs != 'y' or 'n':
        print('That is not a valid option')
        main()

def madLibs():
    madLibs = {1 : 'Today I went to the zoo. I saw a(n) ADJECTIVE jumping up and down in its tree',
               2 : "I walk through the jungle. I take out my ADJECTIVE canteen.",
               3 : 'The day I saw the Monkey King VERB was one of the most interesting days of the year.'}

    randNum = random.randint(1, 3)
    chosenLib = madLibs.get(randNum, 'Entry not found')
    return chosenLib

def replace(para):
    for line in para:
        if 'ADJECTIVE' in para:
            adj = str(input('Type an Adjective: '))
            para.replace('ADJECTIVE', adj)
        elif 'NOUN' in para:
            noun = str(input('Type a Noun: '))
            para.replace('NOUN', noun)
        elif 'VERB' in para:
            verb = str(input('Type a Verb: '))
            para.replace('VERB', verb)
        elif 'ADVERB' in para:
            adv = str(input('Type an Adverb: '))
            para.replace('ADVERB', adv)
        return para

main()

```

The problem is in the `replace` function. Why is it not replacing?