加急!_______THEY HAD TAKEN OFF THEIR SHOSE WERE THEY ALLOWED TO GET INTO THE LAB

题目

加急!_______THEY HAD TAKEN OFF THEIR SHOSE WERE THEY ALLOWED TO GET INTO THE LAB
A.IT WAS NUTIL
B.IT WAS NOT NUTIL
C.UNTIL
D.NOT UNTIL
貌似正确答案是B 麻烦请给解释

答案

选D Not untilNot until they had taken off their shoes were they allowed to get into the lab.意思是：他们不把鞋子脱掉的话是不被允许进入实验室的.因为后面是用的倒装“were they...”故前面应是否定倒装“not...