C. three times as big as
英语中表示倍数的有以下方式:
拿“A比B大几倍来举例”吧
1.比较级:A is several times bigger than B.
2.同级as...as:A is several times as big as B
3.倍数+ 名词:A is several times the size of B
4.用what:A is several times what B is。
楼主的句子用的是第二种句型。
填 C. three times as big as