Suppose you are given the task to sort one thousand 32-bit keys. You have decided to use radix sort for this problem and want to decide how many bits each radix sort digit. Which is best among having 1 bit per radix sort digit, 4 bits per radix sort digit, 8 bits per radix sort digit or 16 bits per radix sort digit? You are provided with a counting sort procedure with exact time complexity of 5n + 4k. Show your work.