是定语从句,a present是表语,后面的空格填which,which引导的从句起的作用就是修饰 a present从句的类型是由从句的位置或者说从句起的作用决定的.从句放在宾语的位置、起宾语的作用就是宾语从句；放在名词/代词之后、...为何不能理解为对宾语a present 进行强调呢？去掉itis....that ......还是一个结构，意思都完整的句子啊。不是吗？如果你改成It was the present that my father bought for me yesterday.那就是强调句型。下面和你说一下定语从句和强调句型的区别：◎强调句中的It没有实际意义，It be与that可同时被省略；而定语从句中的It是主语，It be与that不可同时省略；◎强调句型中be的时态须跟后面句子的时态相一致；而定语从句中主句谓语动词be的时态须由主句的时间确定◎强调句将句子中的that不能省略，并且即使前面的名词是事物时，也不能将that换成which；而定语从句中的that作宾语时可被省略，并且当先行词是事物时可用which代替。◎当it be后面的时间、地点名词作主语、宾语或表语时，引导词可用that / which；而作其他成分时，引导词须用when / which。如：(1) It is an English book (that / which) I bought yesterday. 它是我昨天买的书。(本句是对What is that?问句的回答，that所引导的是定语从句，that可被省略)It was the English book that I bought yesterday. 昨天我所卖的就是这本书。(本句相当于对I bought the English book yesterday中an English book进行强调)(2) It was a room where we used to have meetings. 它是我们过去常在开会的房子。(where 所引导的从句对前面的room进行说明，它是定语从句)It was in the room that we used to have meetings. 过去我们开会就在这间房子里。(in the room是被强调的部分，本句是强调句型)(3) It is a day when the people celebrate their victory. 这是人们庆祝他们的胜利的日子。(when所引导的从句对a day进行说明，是定语从句)It was on that day that people celebrated their victory. 就在那一天，人们庆祝了他们的胜利。(强调on October 1, 1949)