求教 GWD30-2 关于主语表达形式的一个疑点

Q2

Caribou are wary animals with excellent hearing, so stalking them over the treeless landscape, getting close enough to kill it with nothing but a handheld lance, as Dorset people did, required exceptional hunting skill.

1. so stalking them over the treeless landscape, getting close enough to kill it
2. so to stalk them over the treeless landscape and get close enough to kill one
3. so in order to stalk them over the treeless landscape and get close enough to kill one
4. and so in order to stalk it over the treeless landscape, getting close enough to kill it
5. and so stalking them over the treeless landscape and getting close enough in order to kill it

当时因为觉得B项中to do 不能做required的主语所以选择了A,但是答案是B.虽然觉得A项中的It错了,但是对什么样的结构能够作主语产生了模糊:

不是说除了to do is to do以外其他形式下不定式不能做主语吗?另外记得现在分词直接作主语也不是最佳的表达方式.对吗?请指教!

自己顶一下,有谁能够帮我解决一下这个困惑

我觉得这题不是说为了什么什么，然后required什么什么

所以前面应该时表目的的吧，就用to do

个人看法...

doing/doing, to do/to do 这2种时态不能单纯从有没有and去判断，有无and在OG的正确答案里面都有。

A的错误在于：getting close enough to kill it。it显然指代就近对象Caribou。但是Caribou表示该物种的时候显然是复数，it指代有逻辑错误。其次，怎么可能一次消灭整个种族？逻辑上也不通。