How did the Chinese restrict foreign trade during the era 1750–1900?

(A) European merchants were confined to a few cities designated for foreign trade. (B) Only the Dutch traded with China; other Europeans had to use them as intermediaries. (C) The Chinese imposed extraordinary tariffs on all foreign products. (D) They passed laws intended to persecute and harass foreign residents.Explanation: European merchants were indeed closely monitored and their movements restricted to specific areas and cities. Likewise, their exchanges with Chinese people were limited. Both the Portuguese and the British (as well as the Dutch) traded with China (B). Products themselves were limited (C), but they did not carry extraordinary tariffs. Laws were intended only to confine and monitor foreign residents (D).