4 If the following function should return sum of all values from 1 to x, what should replace the missing code? double compute(double x) { } double sum = 0; *** missing code goes here*** O a. for (int i = 1; i <= x; i++) sum += i; return x; b. for (int i = 1; i <= x; i++) sum += i; return sum; Oc. for (int i = 1; i <= x; i++) sum += x; return x; Od. for (int i = 1; i <= x; i++) x + = 1; return x