若直线x+ay-a=0与直线ax-（a-1）y-1=0互相垂直，则a的值是[ ]
A、2
B、-3或1
C、2或0
D、1或0
答案：C
I was very ________when I found that the brake didn't work on my way to the park.[ ]
A. doubtful
B. sensitive
C. scared
D. sympathetic
阿利伯用不同国家的（）来解释国际投资活动。
