Why Did the Number of People Employed in Mexican Maquiladoras

Why did the number of people employed in Mexican maquiladoras begin to drop after 2001?

A) Pull factors in the United States caused many of the workers to migrate there.
B) The Mexican government instituted tougher environmental standards for the maquiladoras.
C) The terms of the North American Free Trade Agreement changed, making the maquiladoras less desirable.
D) China became more popular for labor-intensive work because of its lower wages.
E) The World Trade Organization changed its international labor policies.