1. 情况A：要看看主句是不是一个名词结尾，而这个主句是不是作为从句的主语。如果不是名词结尾，关系代词用which，从句的谓语动词可以用单数
Many employees of small companies have to work very hard, which has become the norm in the workplace.
2、 情况B：写完主句后，如果主句是一个名词结尾，而且从句不管修饰句子还是修饰这个名词都说的过去，这个时候要看名词的性质
️B1 这个名词如果是单数或者是不可数名词
training不可数，谓语动词可以用单数。
Many people today pay attention to on-the-job training, which is important to their career success.
3. B2 这个名词是复数，特别还是表示人的名词，要特别小心处理.尽量使用情态动词，can, may 等，因为情态动词没有单复数，不管修饰前面整个句子，还是前面的复数名词都可
Many people today pay attention to their working relationships, which can be vital to their career achievement.
4. 情况C：如果主句是一个名词结尾，而且从句肯定只可能修饰这个名词，而不可能是前面的句子，这个时候从句的先行词和谓语单复数随着名词变化
这个句子的结尾是historic sites，而且铁定是从句的主语，从句不可能修饰“感兴趣”这个事情。
Many holidaymakers are interested in historic sites, which normally have unique architectural styles.
