Answer: B. High precision.
Answer analysis: When discussing the main features of die-casting boxes, we need to analyze each option one by one and combine the characteristics of the die-casting process to find the most appropriate answer.
A. Lightweight: Although the die-casting process can produce thinner parts, "lightweight" is not an exclusive or main feature of die-casting boxes. Many other manufacturing processes can achieve similar results, so this option is not enough to accurately describe the main characteristics of die-casting boxes.
B. High precision: Die casting is a process in which molten metal or semi-solid alloy is pressed into a mold by pressure and solidified under pressure. Due to the accuracy of the mold and the effect of pressure, die-casting parts usually have high dimensional accuracy and surface finish. This is a significant feature of the die-casting process and a major advantage of die-casting boxes over other manufacturing processes.
C. Good heat dissipation: Heat dissipation mainly depends on the thermal conductivity and design structure of the material, rather than directly determined by the die-casting process. Although some die-casting materials may have good heat dissipation performance, this is not a common or main feature of die-casting boxes.
D. Easy to deform: In fact, die castings should have high strength and stability and not be easy to deform under the correct design, material and process conditions. If die castings are deformed, this is often due to improper design, material selection or process control, rather than the inherent characteristics of the die casting process itself.
In summary, the main feature of the die casting box should be its high precision. This feature stems from the accuracy of the die casting process and the precision of the mold, which enables die castings to have extremely high dimensional accuracy and surface quality.
Therefore, the correct answer is B. High precision.