对C选项的两点困惑:
1.reduces: 觉得用得很好,the 1972 agreement的内容是减少phosphates的量,that是修饰phosphates的,所以reduce用一般现在时(政策、协议的内容/结果用一般现在时)
如:the tax treaty between USA and India reduces the double taxation of income in both countries
2.have been:it is past and continues(from 1972)to the present(动作从1972一直持续到现在)
-------
到底哪错了呢,快被绕晕了!!!