Which is true about isalnum(ch), where ch is an int that

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Which is true about isalnum(ch), where ch is an int that can be represented as an unsigned?
```
 char or EOF.isalnum(ch) returns
```

1. Nothing
2. 0 if not isalpha(ch) or not isdigit(ch)
3. Non-zero if isalpha(ch) or isdigit(ch)
4. Both 0 if not isalpha(ch) or not isdigit(ch) & Non-zero if isalpha(ch) or isdigit(ch)
5. None of these

Correct Option: D

Both 0 if not isalpha(ch) or not isdigit(ch) & Non-zero if isalpha(ch) or isdigit(ch)