- Option (A) is correct because a Jack-up platform has legs that extend to the seabed, which allows it to be elevated above the water. This is typically used in shallow water depths.
- Option (B) is incorrect because a Tension leg platform does not have legs that rest on the seabed; instead, it is anchored to the seabed via tendons.
- Option (C) is correct because a Concrete gravity platform has legs that extend down to the seabed, and it is designed to rest on the ocean floor with the weight of the structure providing stability.
- Option (D) is incorrect because a Semi-submersible platform does not have legs on the seabed; it is a floating platform that is anchored to the seabed but not resting on it.
Thus, the correct answers are options (A) and (C).