def nucleotides_counter(dna):
    """
    Counts DNA nucleotides in a given dna.

    Args:
        dna (str): DNA string (whose alphabet contains the symbols 'A', 'C', 'G', and 'T').

    Returns:
        str: four integers (separated by spaces) counting the respective number of times that the symbols 
        'A', 'C', 'G', and 'T' occur in dna.
    """
    adenine = dna.count("A")
    cytosine = dna.count("C")
    guanine = dna.count("G")
    thymine = dna.count("T")

    return f"{adenine} {cytosine} {guanine} {thymine}"