retained. The major goals of the readjustment process were to expand exports rapidly; overcome key deficiencies in transportation, communications, coal, iron, steel, building materials, and electric power; and redress the imbalance between light and heavy industry by increasing the growth rate of light industry and reducing investment in heavy industry. Agricultural production was stimulated in 1979 by an increase of over 22 percent in the procurement prices paid for farm products. Economist Thomas Rawski summarized China's economic development from 1957 to 1979, writing that "a nation that until 1957 could not manufacture tractors, power plants, or wristwatches now produces computers, earth satellites, oral contraceptives, and nuclear weapons. The technical skills required for industrial development are no longer confined within a few isolated urban enclaves." The central policies of the reform program were introduced experimentally during the readjustment period. The most successful reform policy, the household responsibility system in agriculture, began development in 1979 as a way for poor rural units in mountainous or arid areas to increase their incomes. This system, which came to replace collective farming, maintained public ownership of land and some of the means of production, but made production the responsibility of households. Households still had to contribute to state quotas but could make their own decisions about what to plant on contracted land and could sell via a multi-tier price system that included the lowest price for payment to the state up until the quota, a higher rate for above-quota sales to the state, and market price for crops allowed to be sold at fairs. This multi-tier price system also resulted in price stabilization effects that encouraged production while protecting households from a decrease in market prices caused by the production boom. By 1983, the responsibility system was adopted by numerous farm units in all sorts of areas. Agricultural production was also stimulated by official encouragement to establish free farmers' markets in urban areas, as well as in the countryside, and by allowing some families to operate as "specialized households," devoting their efforts to producing a scarce commodity or service on a profit-making basis. In July 1979, China adopted its first Law on Joint Venture Using Chinese and Foreign Investment. This law was effective in helping to attract and absorb foreign technology and capital from advanced countries like the United States, facilitated China's exports to such countries, and thereby contributed to China's subsequent rapid economic growth.