def support(transactions, itemsets):
    """Returns the percentages of transactions that contain the itemsets.

    Parameters
    ----------
    transactions : list of list
    itemsets : list of frozenset

    Returns
    -------
    dict
        Key of each item is the itemset and the value is the itemset's support
    """
    counts = {}
    for itemset in itemsets:
        counts[itemset] = 0
    for transaction in transactions:
        for itemset in itemsets:
            if itemset.issubset(transaction):
                counts[itemset] += 1
    supports = {}
    total_transactions = len(transactions)
    for itemset, count in counts.items():
        supports[itemset] = count / total_transactions
    return supports