Cycle stealing method: DMA steal for 1 transfer unit (our case character or byte)
240 X 1000 bits
1 sec
30X1000 bytes (or characters)
1 sec
DMA asks CPU for 30000 times
CPU slowed down by

But there is no option
If we assume 240 KBps then
240 X 1000 bytes(or characters)
1 sec
so
Slowed down by

now I am getting the option A