，

more than:超过
was built:被动语态，被建造

112'

It was very difficult to build such a great wall without any modern machines.
without any modern machines:没有任何现代化的机器

173'

52'

thousands of:成千上万
died:死的过去式
while:当...的时候

68'

Have you ever been to...你曾经去过...吗？
foreign:外国的
foreigner:外国人

146'

has a history of over 2000 years:有一段超过两千年的历史
over=more than
not only...but also...不但...而且...
refer to:指

138'

95'