连词前面的逗号问题 while so that
①She is a girl,while I am a boy.②She is a girl while I am a boy.并列连词 while前面可以不加逗号么?还有比如：① people have to spend a great number of time and energy on acquiring advanced skills and knowledge,so that they could retain a competitive edge in job market.② people have to spend a great number of time and energy on acquiring advanced skills and knowledge so that they could retain a competitive edge in job market.so that前面逗号可以省略么?