A、By sending water directly back to the sea with great force. B、By reducing wave energy. C、By reducing beach width. D、By stabili

Your professor has asked me to talk to you today about the topic that should be of real concern to civil engineers: the erosion of the US beaches. Let me start with some statistics. Did you know that 90% of the coast in this country is eroding? On the gulf of Mexico for instance, erosion averages 4 to 5 feet per year. Over the past 20 years, there has been an increase in building along the coast, even though geologists and environmentalists have been warning communities about problems like erosion. Someway, communities have tried to protect their buildings and roads and to build seawalls.
    However, geologists have found that such stabilizing structures actually speed up the destruction of the beaches. These beaches with seawalls, called stabilized beaches, are much narrower than beaches without them. You may wonder how seawalls speed up beach loss. The explanation is simple. If the flow of the beaches is gentle, the water energy is lessened as it washes up along the shore. It is reduced even more when it returns to the sea as it doesn’t carry back much sand. On the other hand, when the water hits the nearly-vertical face of the seawall, it goes straight back to the sea with the full force of its energy and it carries back a great deal of sand. Because of the real risk of losing beaches, many geologists support a ban on all types of stabilizing construction on shorelines.
Questions 33 to 35 are based on the passage you have just heard.
33. Why do communities build seawalls?
34. How does a gently-sloping beach help prevent erosion?
35. What do the geologists advise people to do?