7. (10 points) Jia, Yi, Bing, and Ding all participated in the 100-meter sprint final. Before the race, they made the following predictions:
Jia predicted: “If Bing is 4th, then I will be 2nd.”
Yi predicted: “If Jia is 2nd, then I will be 1st.”
Bing predicted: “Jia and Yi’s performance will either both be better than mine or both be worse than mine.”
Ding predicted: “Jia and Yi’s performance will definitely be one better than mine and the other worse than mine.”
The race ended, and they took the top 4 places (no ties), and each person predicted correctly.
If Jia, Yi, Bing, and Ding placed 1st, 2nd, 3rd, and 4th as $A, B, C, D$ respectively, then the four-digit number $\overrightarrow{\mathrm{BBCD}}=$ $\qquad$
【Answer】Solution: According to the analysis, it is known that Ding's ranking is between Jia and Yi, so Ding definitely cannot be first or fourth, and can only be 2nd or 3rd;

Combining what Bing said, the rankings of the four people can only be “Jia, Ding, Yi, Bing”, “Bing, Jia, Ding, Yi”, “Yi, Ding, Jia, Bing”, “Bing, Yi, Ding, Jia”;

Checking with what Jia and Yi said, it is known that the rankings of the four people can only be $4, 2, 1, 3$.
Therefore, the answer is: 4213.