With direct water cooling it is possible to have ratings of about

The correct answer is B. 300 MW.

Direct water cooling is a type of cooling system that uses water to cool the components of a power plant. The water is circulated through the components and then returned to a cooling tower, where it is cooled by the air. Direct water cooling is a very efficient way to cool power plants, and it is used in many large power plants.

The other options are incorrect because they are not realistic ratings for direct water cooling systems. A 200 MW direct water cooling system would be too small for most power plants, and a 600 MW direct water cooling system would be too large and expensive.

Here is a brief explanation of each option:

• Option A: 200 MW. This is a realistic rating for a direct water cooling system. However, it is not a common rating, and it is not used in many power plants.
• Option B: 300 MW. This is a common rating for a direct water cooling system. It is used in many large power plants.
• Option C: 400 MW. This is a realistic rating for a direct water cooling system. However, it is not a common rating, and it is not used in many power plants.
• Option D: 600 MW. This is too large a rating for a direct water cooling system. It is not used in any power plants.