One of the reasons for the two defenses of mathematical modeling is that there are some problems in your defense. The first defense can't be passed directly, so you need a second defense, that is, a supplementary defense.

The jury will mark your second defense, and then see if you can pass the defense of this national contest on mathematical modeling. Mathematical modeling citizens need a second defense because the first defense is not very good, that is, the questions they answered are not so perfect.

Generally speaking, you can pass the exam with one reply. At the same time, this is the same as thesis defense.

If you can't pass the first defense, you need to make up a second defense in the thesis defense, that is, you need to defend twice.