关于tariff的两道选择题，求解释，在线等，谢谢。-经管之家官网！

Suppose the United States eliminates its tariff on ball bearings used in producing exports. Ball
bearing prices in the United States would be expected to
(a) increase, and the foreign demand for U.S. exports would increase.
(b) decrease, and the foreign demand for U.S. exports would increase.
(c) increase, and the foreign demand for U.S. exports would decrease.
(d) decrease, and the foreign demand for U.S. exports would decrease.
(e) None of the above.
Answer: C
为什么是C呀？不是export的成本下降，价格下降吗？
此外，这句话为什么对？
Tariffs are not defended on the ground that they improve the terms of trade of foreign nations.
关税不是会恶化外国的Terms of trade 吗？
The tariff levied in a large country (home) ,lowers the world price of the imported good. This causes
A.domestic demand for imports to decrease.
B domestic demand for imports to increase.
C.foreign suppliers to produce less of the good on which was levied a tariff.
为什么选C而不选A呢？是因为A中的import包括所有的进口商品吗？
还有一点：The fact that industralized coutnries levy very low or no tariff on raw material and semi processed goods:
C.hurt develping country efforts to export manufactured goods.
为什么选C呢？我的思路还是觉得成本降低了，所以对出口有利？请问错在哪呢？
求解释谢谢！