To distinguish modular bricks from traditional bricks, we need to understand the characteristics and production methods of each type:

• Modular Bricks: These bricks are produced with standardized dimensions. The major advantage of modular bricks is that all construction elements such as masonry walls, doors, and windows are designed in increments of the same module. This standardization leads to reduced wastage, easier transportation, and efficient construction processes.
• Traditional Bricks: These bricks do not have standardized dimensions and therefore can vary significantly in size. They are often used in construction that does not require strict standardization or where local materials are available in specific sizes.

The question asks about the primary distinction between modular and traditional bricks. Among the provided options, the correct answer is:

Modular bricks are produced with standardized dimensions.

Let us analyze why the other options are not correct:

• Traditional bricks are produced in larger standard sizes: This is incorrect because traditional bricks do not adhere to standardized sizes and can actually vary in size.
• Modular bricks are manufactured mainly by manual methods: This is incorrect because modular bricks are often produced using both manual and automated processes to maintain consistent quality and dimensions.
• Traditional bricks are manufactured using lightweight materials: This is incorrect because traditional bricks are generally heavier due to their size and production method. They are not necessarily manufactured using lightweight materials.

In conclusion, the defining feature of modular bricks is their standardized dimensions, enabling efficient construction and adherence to engineering and architectural standards.