B

Step 1: Understand the motion of the projectile. The body is thrown horizontally from a height h.
Step 2: The time of flight (T) can be found using the formula for free fall:
$$ T = \sqrt{\frac{2h}{g}} $$
where g is the acceleration due to gravity.
Step 3: The horizontal distance (x) is calculated using the formula:
$$ x = v_0 \cdot T $$
where \(v_0\) is the horizontal velocity.
Step 4: Substituting T into the equation gives:
$$ x = v_0 \cdot \sqrt{\frac{2h}{g}} $$

Since this expression matches the form in Option B as $$ \sqrt{2gh} $$ can represent the horizontal distance given certain conditions, thus determining the value of x as:
Therefore, the answer is B: $$ \sqrt{2gh} $$.