单选题：以下程序段（ ）不能实现求s = 1+2+...+n-1。

以下程序段（ ）不能实现求s = 1+2+...+n-1。 @[B](1)

A.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = 1; i < n; i++ ) {
s = s + i;
}
```
B.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = n-1; i > 0; ++i ) {
s = s + i;
}
```
C.
```
int i, n, s = 0;
scanf("%d", &n);
for (i = n-1; i > 0; i-- ) {
s = s + i;
}
```
D.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = 1; i <= n-1; ++i ) {
s = s + i;
}
```






A.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = 1; i < n; i++ ) {
s = s + i;
}
```
B.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = n-1; i > 0; ++i ) {
s = s + i;
}
```
C.
```
int i, n, s = 0;
scanf("%d", &n);
for (i = n-1; i > 0; i-- ) {
s = s + i;
}
```
D.
```
int i, n, s = 0;
scanf("%d", &n);
for ( i = 1; i <= n-1; ++i ) {
s = s + i;
}
```


答案：B