求助 GWD30-2

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

正确答案是B，可是这样不是and前后不对称，一个是不定式一个是动词原形