Steel tanks are mainly designed for A. Weight of tank B. Wind pressure C. Water pressure D. Earthquake forces

The correct answer is: C. Water pressure.

Steel tanks are mainly designed to withstand the pressure of the water they contain. The weight of the tank itself is also a factor in the design, but it is usually less important than the water pressure. Wind pressure and earthquake forces are also considered in the design of steel tanks, but they are usually not as critical as water pressure.

Here is a brief explanation of each option:

• Option A: Weight of tank. The weight of the tank itself is a factor in the design, but it is usually less important than the water pressure. The weight of the tank is determined by its size and the material it is made of.
• Option B: Wind pressure. Wind pressure is a force that acts on the surface of the tank. The wind pressure is determined by the speed of the wind and the area of the tank.
• Option C: Water pressure. Water pressure is a force that acts on the walls of the tank. The water pressure is determined by the depth of the water and the area of the tank.
• Option D: Earthquake forces. Earthquake forces are forces that act on the tank due to the movement of the earth. The earthquake forces are determined by the magnitude of the earthquake and the distance of the tank from the epicenter of the earthquake.