The function takes an input string and returns a string containing the English words for any numbers present in the input string.

[CODE]: 
```python
def number_to_words(s):
    num_to_word = {
        "0": "zero", "1": "one", "2": "two", "3": "three", "4": "four", "5": "five",
        "6": "six", "7": "seven", "8": "eight", "9": "nine"
    }
    result = []
    for char in s:
        if char in num_to_word:
            result.append(num_to_word[char])
    return " ".join(result)
```