插入语是不是一般都要用逗号隔开?

1.插入语在句中,一般是要用逗号和句子其他成分隔开的.
如：
1）Strange to say,he hasn’t got my letter up to now.
说来也奇怪,他到现在还没有收到我的信.
2）When he got there,he found,however,that the weather was too bad.
可是到了那儿之后他发现,那儿的天气太坏了.
3）You can’t wait anymore-in other words,you should start at once.你不能再等了——换言之,你得立即出发.
4）Generally speaking,the weather there is neither too cold in winter nor too hot in summer.
一般来说,那儿的气候冬天不太冷,夏天不太热.
5）To tell you the truth,I’m not so interested in the matter.
跟你说实话,我对这件事情的兴趣不大.
2.但是,像do you think之类的插入语是可以直接放在句中的疑问词之后的,可以不用逗号隔开.
如：What do you think I should do first?你认为我应该先做什么?
Who do you think is singing?你认为是谁在唱歌?