China's exports to the United States are consumer goods, such as clothing and textiles, household goods, toys and shoes. The products exported by the United States to China are high-end manufacturing products. There are differences between Chinese and American economies. Option a is correct. The United States is a developed country, while China is a developing country. The products exported by developed countries have higher technical content than those of developing countries. Option b is wrong. China exports consumer goods to the United States, and the United States exports high-end manufacturing products to China. These two economies complement each other. Option c is correct. The United States trades with China.

Therefore, choose: d.