A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities are/were allowed to dump into the great lakes.
如果有have been allowed 这个选项会比are allowed/were allowed 好么??前者不是强调从以前一直到现在一直持续的状态么??还是说因为这是个agreement所以只能用一般过去或者一般现在时?、
A 1972 agreement between Canada and the United States reduced the amount of phosphates that municipalities are/were allowed to dump into the great lakes.