应该是a useful。单词前用a还是an,这取决于该单词音标中第一个音是辅音还是元音,useful的音标是['jusfl],音标中第一个音是“j”,是辅音,所以用a,而不是用an。useful前用a。接a还是an,看后面的单词第一个音标是辅音还是元音,useful的音标为[`ju:sful],所以接a。
But I think even NLTK's lower layers make it a useful framework for both pedagogical and practical applications.
不过,我认为,即使是NLTK较低的层,也可以成为一个既可用于教学应用程序也可用于实际应用程序的实用框架。
It's common to think of the breath as the air passing in and out through the nose, and this can be a useful perception to start with.
一般认为气是指出入鼻腔的气息,可以把这个辨识当作有用的起点。
A useful approach to creating tables is to create a basic table, add some data to it, and then work with it for a while.
创建表的有用方法是:创建一个基表,向其中添加一些数据,并使用这个基表一段时间。
a useful book一本有用的书;单词useful以元音字母u开头,但它的读音以辅音音素/ju:/开头,所以前面用a;This is a very useful book of cloud computing , I think all of us must help.
这是一本很有用的云计算书籍,我认为一定对大家有帮助。