Chairman mao

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Chairman mao who gave a speech on October 1st,1949 was our great leader.
大意：在1949年10月1日做演讲的毛主席是我们伟大的领袖.
Chairman mao was our great leader 是主句
_____ gave a speech on October 1st,1949 便是从句,这个从句修饰了主语Chairman mao,所以它是定语从句
根据句子完整性来看,在这个从句中,动词gave前方没有主语,（只有一条横线不是~）即是缺主语,并且主语是人,所以我们在gave前加上人称主格 who