问题补充：
You’d better go there by train. The train ticket is the plane ticket.
A. as cheap three times as
B. as three times cheap as
C. three times cheaper than
D. cheaper three times than
答案：
A. as cheap three times as
B. as three times cheap as
(答案→)C. three times cheaper than
D. cheaper three times than
解析：考查倍数表达。倍数表达的基本结构：
1. “A+倍数+形容词或副词的比较级+than+B”，表示“A比B大（长、高、宽等）多少倍”。
2.“A+倍数+as+形容词或副词的原级+as+B”，表示“A正好是B的多少倍”。
3. “A+倍数+the size/height/length/width， etc+of+B”，表示“A正好是B的多少倍”。
4. “……times+what+从句”。
选项ABD结构有误，故选C。
