this is the last lesson which mr smith taught me.
正确的应该是:
this is the last lesson that mr smith taught me.
因为先行词lesson被最高级the last修饰,关系代词只能用that,不能用which
this is the last lesson which mr smith taught me.
正确的应该是:
this is the last lesson that mr smith taught me.
因为先行词lesson被最高级the last修饰,关系代词只能用that,不能用which