Which of the following structure is correct for WHILE loop?

The correct structure for a WHILE loop in most programming languages is:

while (condition) {
  // code to be executed
}

Here's how it works:

1. The while keyword starts the loop.
2. The condition for the loop is specified in parentheses. This condition is checked before each iteration of the loop. If the condition is true, the loop will continue; if it's false, the loop will end.
3. The code to be executed in each iteration of the loop is enclosed in curly braces {}.

Here's an example in JavaScript:

let i = 0;
while (i < 5) {
  console.log(i);
  i++;
}

This code will print the numbers 0 through 4 to the console. The loop continues as long as i is less than 5.