听力原文：I want to talk today about some studies. They seem to indicate that there is a st

听力原文： I want to talk today about some studies. They seem to indicate that there is a startling world-wide decline in the number of amphibians, such as frogs, toads and salamanders. There's little doubt that one reason why the number of amphibians is declining is their habitats have been destroyed when the developers fill in ponds and marshes to build houses. Amphibians can't just move somewhere. They need water to lay their eggs in. Another problem is the growing fish industry. Another range of popular pool fish such as carp have been introduced to many lakes and ponds all over the world. Raising and selling these fish can be profitable, but the fish eat the eggs and offspring of amphibians that were already living in the lakes and ponds. Other factors could be contributing to the decline include acid rain and the spread of pesticide residues. Many pesticides that farmers added to their crops are eventually washed away by the rain and end up in ponds and other bodies of water where amphibians live. Amphibians are especially vulnerable to pesticides dissolved in the water because of their moist skins. Water can pass through amphibians allowing toxins dissolved in the water to enter the amphibians' body.

What does the speaker mainly discuss？

A．The distribution of different species of amphibians.

B．Possible reasons for reduction in the number of amphibians.

C．The effects of environmental change on the fish industry.

D．Guidelines for the responsible use of pesticides.