Bob is six years old．He is old enough to go to school． On the first day，his teacher taught him three words，“I，you，he”．Then the teacher said，“I am your teacher．You are my student．He is your student. He is your classmate.”When school was over，Bob went home. His mother asked him，“What has your teacher taught you today?”Bob said with a smile，“Listen，Mum and Dad，I am your teacher．You are my student．He is your classmate．”His mother said，“No，dear．You’re wrong．”Then she said，“I am your mother．You’re my son．He’s your father．”The next day，Bob’s teacher asked Bob to make sentences with “I，you and he”．
Bob stood up and said，“I’m your mother．You’re my son．He is your father．”All the students in Bob’s class laughed．

①上调房产税率→购房成本减少→购房需求下降→房价下跌

②保障房建设→住房供给增加→住房供求矛盾缓解→房价下跌

③居住用地供应增加→建筑成本降低→住房供过于求→房价下跌

④利率上调→购房成本增加→购房需求下降→房价下跌