（1）表示原因的连接词
for this reason, due to, thanks to,
because, because of, as, since, owing to.
（2）表示结果的连接词
as a result, thus, hence, so, therefore,
accordingly, consequently, as consequence.
（3）用于总结的连接词
on the whole, in conclusion, in a word, to sum up,
in brief, in summary, to conclude, to summarize, in short.
