The correct answer is: A. Ordinary Portland cement
Ordinary Portland cement (OPC) is the most common type of cement used in construction. It is a basic ingredient in concrete, mortar, and grout. OPC is made by heating limestone and clay to high temperatures, and then grinding the resulting clinker into a fine powder.
OPC is suitable for use in massive concrete structures such as large dams because it is strong and durable. It is also relatively inexpensive and easy to use.
Low heat cement is a type of cement that produces less heat when it is mixed with water. This makes it less likely to cause cracking in concrete structures. Low heat cement is often used in large concrete structures, such as dams and bridges.
Rapid hardening cement is a type of cement that sets and hardens more quickly than ordinary Portland cement. This makes it useful for applications where early strength is required, such as in precast concrete.
Sulfate resisting cement is a type of cement that is resistant to attack by sulfates in the environment. This makes it suitable for use in concrete structures that will be exposed to sulfates, such as those in coastal areas.
In conclusion, ordinary Portland cement is the most suitable type of cement for use in massive concrete structures such as large dams. It is strong, durable, relatively inexpensive, and easy to use.