A sample of 1 mol chains of $100000\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$ is mixed with 1 mol of short chains of $1000\mathrm{g}\mathrm{mo}{\mathrm{l}}^{-1}$. Compared with the original sample, which are correct?

1. A$M_n$ falls to about half of its original value
2. B$M_w$ changes by less than 2 percent
3. CThe PDI of the mixture exceeds 1.9
4. D$M_w$ falls to about half of its original value