A9. On a certain lake, the lily pads grow in such a way that there are twice as many of them every day. On Wednesday, a quarter of the lake was covered. When will the entire lake be covered?
(A) on Thursday
(B) on Friday
(C) on Saturday
(D) on Sunday
(E) on Monday
A9. Since on Wednesday a quarter was covered and the lilies double every day, there will be $2 \cdot \frac{1}{4}=\frac{1}{2}$ of the lake on Thursday, and on Friday $2 \cdot \frac{1}{2}=1$, thus the entire lake.