气温影响空气密度，气温高，空气密度小，则声速大，因而声速与气温有关，由此产生的声音不一定由声源沿直线传播．晴天的中午，地表迅速升温，地表附近的气温较上层的气温高，声音在地表附近的传播较上层快，于是在地面上的声源发出的声音向四周传播时是向上拐弯的，弯到温度低，密度大的上方．

根据以上信息回答：

（1）声音在空气中传播时，爱走温度 ____、密度 ____的路径；

（2）“姑苏城外寒山寺，夜半钟声到客船”说的是：在清冷的深夜，姑苏城外寒山寺的钟声因传播的途径向 ____拐弯而传到几里外的枫桥边．

（3）赤日炎炎，在沙漠或戈壁滩即使相距不太远的人也难听清对方的大声叫喊，其中一个重要的原因是声音在传播时向 ____拐弯了．

短文改错

    My friend Henry, with who I studied in the same class, didn't like studying at school. That's because he couldn't go to high school. He had to return back to his hometown, where his father wished him to learn to manage our small shop. However, the young man was not interesting in it and didn't do as his father said. He spends a lot of time reading and he also learned how to repair cars. Last month, I received an e-mail from him inviting me take my vacation on his hometown. I started off. Seeing that he was such successful, I said, “Henry, all road lead to Rome. You are great!”

①一种化合物  ②两种单质  ③两种化合物  ④一定是氧化物．

有关生物学实验或调查的叙述，正确的是（　　）