You are teaching beginners A, B, C at your company.

You are teaching beginners A, B, C at your company. The beginners wrote the following functions. These functions receive an array of integers a and outputs the sum of all elements in array a.

Choose all functions that work properly. At least 1 function works properly.

Beginner A

function sum(a) {
    let answer = 0;
    for (let i = 0; i < a.length; i++) {
        answer += a[i];
    }
    return answer;
}

Beginner B

function sum(a) {
    let answer = 0;
    for (let i = a.length; i > 0; i--) {
        answer += a[i];
    }
    return answer;
}

Beginner C

function sum3(a) {
    let answer = 0;
    let i = 0;
    while (i) {
        if (i == a.length) {
            break;
        }
        answer += a[i];
        i++;
    }
    return answer;
}