---This is useful machine which was made in thirteenth century A. a theB. an theC. / t

问题补充：

---This is useful machine which was made in thirteenth century

A. a, the

B. an , the

C. /, the

D. the , /

答案：

(答案→)A. a, the

B. an , the

C. /, the

D. the , /

解析：句意: -这是一台有用的机器，它是在13世纪制造的。本题考查冠词，第一空的a 是来修饰machine的，是一个可数名词的单数形式，故用a ；第二空是说13世纪，前应用定冠词the 。故选A。