John, who was lazy, scored quite high marks on the exam, which somewhat surprised me.
Which代替整句,which之前要逗點。約翰很偷懶卻考相當高分,這使我有些驚訝
He smokes three packs of cigarettes a day, which definitely does harm to his health.
Which代替前面句中部分概念,which之前要逗點。他每天抽三包菸,這對他的健康一定有害