Which of the following could be counted by calculating ? (Check all that apply.) Group of answer choices The number of 4-element subsets of the set {$, %, 2, 3, 4, +, &} The number of ways to arrange exactly 4 ones in a string of 7 binary digits The number of bit strings of length 4 and weight 7 The number of 7-element subsets of the set {a, $, 4}