No one knows for certain what happened, but it's a fair bet that it was not an accident.
没有人知道究竟发生了什么,但几乎可以肯定这并非意外。
the first group began to show some personality disorders while the others seemed more or less unaffected.
结果,第一组人开始出现性格失常,而第二组人似乎没受什么影响。