请教一道简单题 OG-11/Review/SC-4

原题

A survey by XXX showed that in 1986 there were 20,736 female ministers, almost 9 percent of YYY, twice as much as 1977

正确选项是double the figure for 1977

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排除法很容易得知其他四个选项是错误的; 不过，上面正确的选项 --- double是动词还是形容词呢？

（1）如果是动词，显然时态和showed/were不符，且句意错误（不能是survey或者there去double）

（2）如果是形容词，倒装？为什么？句型复原后是什么？

多谢！