After a long while, ( ),because no one knew whether the cave they found ...下列选项哪个正确

After a long while, ( ),because no one knew whether the cave they found ...下列选项哪个正确
After a long while, (),because no one knew whether the cave they found was a cache of treasure or a secret deposit of dangerous arms left over from the last war.
A two bold villagers went very cautiously into the cave
B this cave was being very cautiously gone into by two bold villagers
为什么选A不选B