12. (12 points) In the garden, there are sunflowers, lilies, and peonies.
(1) There is only one day in a week when all three flowers bloom simultaneously;
(2) No flower blooms for three consecutive days;
(3) In a week, there will not be more than one day when any two flowers do not bloom;
(4) Sunflowers do not bloom on Tuesday, Thursday, and Sunday;
(5) Lilies do not bloom on Thursday and Saturday;
(6) Peonies do not bloom on Sunday;
So, on which day of the week do the three flowers bloom simultaneously?
【Answer】Solution: According to the given conditions:
A chart can be made as follows:
\begin{tabular}{|c|c|c|c|c|c|c|c|}
\hline & Monday & Tuesday & Wednesday & Thursday & Friday & Saturday & Sunday \\
\hline Lily & & & & $X$ & & $X$ & \\
\hline Sunflower & & $X$ & & $X$ & & & $X$ \\
\hline Peony & & & & & & & $X$ \\
\hline
\end{tabular}

Therefore, the three flowers bloom simultaneously on Monday.
The answer is: Monday.