Which of the following segments is a proper way to call the method readData four times?

a. double k = 0.0;

while (k != 4)
{
readData();
k = k + 1;
}
b. int i = 0;

while (i <= 4)
{
readData();
i = i + 1;
}
c. int i = 0;

while (i < 4)
{
readData();
}
d. int i = 0;

while (i < 4)
{
readData();
i = i + 1;
}

d. int i = 0;

while (i < 4)
{
readData();
i = i + 1;
}