On this issue, assuming that the volume of the container is V, the concentration becomes:
(09.V-0.9)/V
After the second filling and filling, the concentration becomes:
[0.9V-0.9-(0.9V-0.9)/V]/V = 0.9(V- 1)? /V? V=3 can be obtained by =0.4, so the answer is B. Regarding the real questions related to MBA, I suggest you read the book "Analysis of Mathematics Real Questions over the Years" written by Teacher Shi Peng, and the answer is still very detailed.