It is doubtful that he will come.

他会不会来值得怀疑。

It is doubtful that any foreign leader since has spent more time as a guest at the White House.

自此之后，是否有哪位外国领导人在白宫度过比这更长的时间令人怀疑。

Some 75% of all international communications are in English, and with the rise of the Internet, it is doubtful that this figure will decrease any time soon.

大约有75%左右的国际性交流以英语进行，而且随着互联网的兴起，这个数据恐怕短时间内是不会降低的。

And it is doubtful that governments can do all that much to alter social norms, just as they hold little responsibility for the fact that they changed in earlier decades.

政府能否做出如此大的努力来改变社会规范是值得怀疑的，就像他们对自己在前几十年发生的改变几乎不承担任何责任一样。