基数词在表示确切的数字时,不能使用百、千、百万、十亿的复数形式,而是直接用在数量的后面,如3 hundred, 5 thousand, 7 million, 9 billion；
但是,当基数词表示不确切数字,如成百、成千上万,三三两两时,基数词则以复数形式出现,如：hundreds of , thousands of, millions of 意思是：数以百计的,成千上万的,上百万的,
There are hundreds of people in the hall．
大厅里有数以百计的人.
Thousands and thousands of people come to visit the Museum of Qin Terra-Cotta Warriors and Horses every day．
每天有成千上万的人来参观秦兵马涌博物馆.
They went to the theatre in twos and threes．
他们三三两两地来到了剧院.
这题并不是表示成千上万的意思 所以应该选第二个
two thousand of
clear now?