Step 1: Analyzing the types of dams.
- (A) Gravity dams are rigid concrete or masonry structures that resist water pressure primarily through their own weight.
- (B) Arch dams are typically built on very strong, stable foundations, as they rely on the strength of the rock to support the structure.
- (C) A buttress dam has a watertight upstream face (typically a sloped concrete slab) supported by downstream buttresses.
- (D) Earth dams typically have a sloped surface, not a concrete wall. Their structure is not curved in the manner described.
Step 2: Conclusion.
Answer: (A) and (C) are correct