Generally speaking, the primary industry acts as a "reservoir" for surplus labor. Although the surface can absorb a large amount of labor, it actually has limited capacity to absorb it. The second and third industries are the main industries that absorb labor. Under the same economic scale (that is, the same GD. P), the higher the proportion of the secondary and tertiary industries, especially the tertiary industry, the greater the carrying capacity of the labor force in a certain region. What does this text mainly explain? ['The limited ability of the first industry to effectively absorb labor.', 'Different regional industrial structures have different labor force carrying capacity.', 'Second, the tertiary industry is the main industry to absorb labor, and it should focus on the development.', 'The economic scale has a large impact on the carrying capacity of the labor force.']