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

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