The condition of workers in this country has improved greatly.
此句中的副词（greatly）就是位于句末,修饰动词improve.这句话强调的是动词improve,注意下面这句话：
The condition of workers in this country has greatly improved.
这句话和上面一句话表达是同一种意思,但强调的是greatly程度.
英语中副词一般修饰动词和形容词,不能直接跟在Be动词后面.
I am terribly sick of seeing a snake.
Police directly went up stairs in search of the murder.
明白了不?