for后面可以加原因,for在句中
如We must start early,for it will take two hours to drive to the airport.这里for是连词,连接两句句子
又如I am sorry for what I said to you.
for是介词
by的意思是通过...的方式/方法,一般指...通过这个方法达到...目的,但本句没有人们刻意为之的意思
as是连词,但这里the rapid growth of short messages sent by cellphones不是句子
With the rapid growth of short messages sent by cellphones,the increasing number of criminal cases appeared through short messages.
随着用手机发的短信的迅速增长,用短信犯罪的人也越来越多.