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。
If we remain inveterate smokers, it is only because we have so often experienced the frustration that results from failure.
如果我们烟瘾大,戒不掉,那是因为屡戒屡败,失去信心。