Firstly, the author suggests that a national fence should be built. However, the lecture opposes this suggestion by saying that young toads and toad eggs are found in rivers and streams that would carry them to the other side, no matter where the fence is built / regardless of the fence. As a result, the population will continue to grow.

　　Secondly, the passage proposes that volunteers can trap and destroy cane toads. However, the speaker views this issue from an opposite angle. According to her/him, untrained volunteers tend to inadvertently destroy endangered frogs since it is hard to distinguish (tell A apart from B) them when they are young.

　　The third measure (proposed by the writer) is to develop a disease-causing virus. By contrast, in accordance with the professor, this method does not hold water. It is because cane toads (infected by the virus) would be transported to Americas (where the local cane toad is a vital part of the ecosystem). Once the virus attacks them, the local ecosystem would suffer.

　　R: the reading material, writer, author, passage

　　L: the listening material, speaker, lecture, lecturer, professor

　　认为： point out, state, claim, argue, hold,/ propose, put forward, suggest

　　反驳、反对：disagree with, disapprove of, object to, reject, rebut, refute, contradict, oppose/ cast doubt on, challenge, question