A

Step 1: Understand Gauss's Law, which states that the net electric flux through a closed surface is directly proportional to the charge enclosed within that surface.
Step 2: Here, we note that the lines leaving the surface are double the lines entering it. Let the number of lines entering the surface be \( N \), then the number of lines leaving the surface is \( 2N \).
Step 3: The net electric flux through the surface can be calculated as:
\[ \Phi_E = \text{(lines leaving)} - \text{(lines entering)} = 2N - N = N \]
Step 4: Since the net electric flux \( \Phi_E \) is proportional to the charge enclosed, we conclude that there is a positive charge inside the surface.
Therefore, the nature of charge enclosed by the closed surface is positive.