Zhang Tian graduated from university and got a teacher's certificate last year.

这是简单句。并列连词只有连接两个不同的句子，即：主语和谓语动词各不相同的两个分句，才是并列句。
如果：同一个主语用两个不同的谓语动词，或者两个不同的主语用同一个谓语动词，都不是并列句。如果两个主语用两个不同的谓语动词，或者分别用相同的一个谓语动词，才是并列句。例如：

Zhang Tian graduated from university and got a teacher's certificate last year. （简单句）

Zhang Tian and Tom graduated from university.（简单句）

Zhang Tian likes music and Tom is fond of football. （并列句）

Zhang Tian graduated from university and Tom graduated from university, too. （并列句）

即便下面这个句子，也是简单句：

Zhang Tian and Tom graduated from university and got a teacher's certificate last year. （简单句）

加上主语就是并列句：

Zhang Tian and Tom graduated from university and they got a teacher's certificate last year.（并列句）