In modern era, it’s unlikely for a nation to produce everything (it needs) and consume everything (it makes). To alleviate the dilemma of surplus and shortage, goods are exchanged between nations. … A country might prohibit importing or exporting certain products, or it might set quotas controlling the number of certain products to be imported or exported, or it might charge duty tax on certain products. …
 
参考译文
在现代，一个国家不太可能生产出自身所需要的一切，也不太可能消费掉自己能够生产出的一切。为了缓解剩余与短缺之间的这种两难局面，国与国之间都在进行货物交换。……一个国家可能禁止进口或出口某些特定的产品，也可能制定配额用以控制某些进出口产品的数量，同时还可能就某些产品征收进口关税。……
 
1、be likely/ unlikely to do sth.；be likely/ unlikely that（不）可能的，如：He is not likely to succeed.他大概不会成功。It’s highly likely that he will succeed.他成功的可能性很大。
2、alleviate v.减轻，如：The UN’s most important objective is to alleviate world poverty.