根据教授所说：Two factors were important for lake formation in the Empty Quarter. First, the rains that fell there were torrential. So it would've been impossible for all the water to soak into the ground. Second, as you know, sand dunes contain other types of particles, besides sand, including clay and silt. 据此可知，湖泊形成有两个重要因素，一是雨量特别充足, 不至于所有的雨水全部渗入地下；二是沙丘中除沙子外，还含有粘土和淤泥，可以储水，对应 B 选项说法，所以本题选 B。

答案: B