为什么第一句话free trade但又不是free trade area

问题如下：

If Brazil and South Africa have free trade with each other, a common trade policy against all other countries, but no free movement of factors of production between them, then Brazil and South Africa are part of a:

选项：

customs union.

common market.

free trade area (FTA).

解释：

A is correct.

A customs union extends a free trade area (FTA) by not only allowing free movement of goods and services among members, but also creating common trade policy against non-members. Unlike a more integrated common market, a customs union does not allow free movement of factors of production among members.

考点：free trade area

自由贸易只要求商品的自由流动，C选项不入选。

common market仅仅还要求贸易国间的生产要素能够自由流动，所以B选项不入选。