单选题
The touch excites no defensive response unless the approach is from above where the spider can see the motion,______on its hind legs, lifts its front legs, opens its fangs and holds this threatening posture as long as the object continues to move.(中国社会科学院2006年试题)
【正确答案】
A
【答案解析】解析：本题中空格处的意思是“在何种情况下它举起它的后腿”。in which case指代的是前面句中所述情况，无需倒装，因此A项为正确答案。