What is the fine-grained topic of the following text: In response to the US threat of an additional 25-percent tariff on Chinese imports worth about US$50 billion earlier this month, China has announced that additional tariffs for 545 items worth about 34 billion dollars, including agricultural products, vehicles and aquatic products, will be effective from July 6. Only return the topic.
China's response to US threat of additional tariff on Chinese imports