A is correct. Additional collateral (C) required for posting can be explained from the mark-to-market value of collateral posted (X), mark-to-market value of net exposure (E), the threshold (K), and the minimum transfer amount (MTA) as follows:
(i) Collateral call (C) can be made if: $E > (K + \text{MTA} + X)$
(ii) The collateral amount required: $C = E - K - X$, and the amount is positive if $(E - K - X) > \text{MTA}$, otherwise it is zero.

In this example:
$(K + \text{MTA} + X) = 14,000,000 + 2,500,000 + 10,800,000 = 27,300,000 > E = 27,000,000$
which corresponds to no collateral call. Thus, A is correct.

B is incorrect. CNY 1,990,000 = new exposure − original exposure − rounding amount = $27,000,000 - 25,000,000 - 10,000$, which is incorrect.

C is incorrect. CNY 2,000,000 is the difference between the new net exposure and the original net exposure ($= 27,000,000 - 25,000,000 = \text{CNY } 2,000,000$).

D is incorrect. CNY 2,500,000 is the minimum transfer amount.