Question: Which is _not_ a valid loop construct in Go?

1. `do { ... } while i < 5`
2. `for _,c := range "hello" { ... }`
3. `for i := 1; i < 5; i++ { ... }`
4. `for i < 5 { ... }`

Answer: The correct answer of the above question is Option A:`do { ... } while i < 5`