TOEFL Reading: ETS-TOEFL阅读机经 - YTN634ZP306BV49CL$

According to paragraph 2, protective levees can have which of the following disadvantages? A. They can greatly increase the destruction caused by floodwaters when floodwaters are higher than the levee. B. They can fail even when the flood level remains below the height of the levee. C. They can lead over time to a serious salinization problem. D. They can cause damaging floods to occur more frequently by changing basic water patterns.