Nobody except Xiao Liu and Xiao Wang knows her parents.
What we need at present is science and technology.
Reading English magazine and novel is helpful to youe study of English.
Our master and group leader often helps us.
我想问下except 是强调前面的,还是后面的,为什么要用knows;
是不是因为科学和技术不可数就用is;
第三句为什么用is;
第四句既然有and,为什么不是help,而是三单形式?
谢谢!
参考资料:Baidu knows