【正确答案】The professor talks about two benefits of planting trees in the city, although city is a busy and overcrowded place.
First, building trees is beneficial to the urban environment by absorbing carbon dioxide released from cars. According to the lecture, carbon dioxide emission, in large part, from the cars not only produces pollution in the air, but also leads to global warming because of the greenhouse effect. However, trees can help absorb carbon dioxide emitted from cars and thus reduce air pollution. The more trees there are, the more oxygen there is to breathe, too.
Another benefit is that trees store water from the rain. Since trees release the water into the air slowly, the rainfall would not touch the ground and evaporate immediately. This means trees help increase humidity and add moisture to the environment.

【答案解析】 讲座描述了在城市中植树的两个好处，即“The professor talks about two benefits of planting trees in the city．”