问题补充：
They have stayed in Beijing for .
A. one and half an hour
B. one and a half
C. one year and a half
D. one and a half hour
答案：
A. one and half an hour
B. one and a half
(答案→)C. one year and a half
D. one and a half hour
解析：句意：他们已经在北京住了一年半了。一年半one year and a half固定表达，也可以说成one and a half year两种表达都行。故选C.
