DMA usually operates in cycle stealing mode, where it transfers 1 byte per cycle. //Default assumption.
So, given DMA bandwidth = 9600bps = 1200 bytes per sec.
1 MIPS = 1 Million Instructions Per Second.
So, normally, CPU fetches $10^6$ instructions each second.
Now, CPU can fetch $10^6 - 1200$ instructions per second. //Assumption 1 instruction = 1B
Rate of change = $\frac{10^6-(10^6-1200)}{10^6}$ = $\frac{1200}{10^6}$ = $1.2*10^{-3}$
Option D