Let BT for A is x
Let BT for C is y
As A runs for 7 units, remaining time of A is x-7
As it is SRTF and the process C preempts A therefore, x-7>y
C runs for 1 unit of time,then B preempts C
similarly, y-1>2
y is greater than 3 ,y is 4 than x is 12
ANS: d