1.当定语从句的引导词在从句中作主语时，定语从句中谓语动词的形式是根据先行词而定的。
【误】People who has been invited to the party are very excited.
【正】People who have been invited to the party are very excited.
【析】例句中who在定语从句中作主语，先行词是people，从句中谓语动词要用have been invited。
2.主语是单数时，尽管后面跟有with，together with，but，except，besides，as well as等介词短语，谓语动词仍用单数形式。
【误】Mary,with her brothers,study Chinese in China.
【正】Mary,with her brothers,studies Chinese in China.
【析】Mary在句中是主语，谓语动词要用studies，而不用study。
3.表示学科名称的名词maths、physics等为单数名词，news为不可数名词，他们在句中作主语时，谓语动词都应用第三人称单数。
【误】Physics are difficult for him.
【正】Physics is difficult for him.
【析】physics在句中作主语为单数名词，谓语动词应用第三人称单数is。
