The compressibility factor $Z$ of a gas is $0.9800$ at $10.0\mathrm{atm}$ and $300\mathrm{K}$ and the dependence is linear in $P$ in this region ($R=0.0821\mathrm{L}\mathrm{atm}{\mathrm{K}}^{-1}\mathrm{mo}{\mathrm{l}}^{-1}$). Which statements are correct?

1. AAt $20.0\mathrm{atm}$ and $300\mathrm{K}$, $Z$ is about $0.960$
2. BThe slope $dZ/dP$ is $-2.00\times 10^{-3}\mathrm{at}{\mathrm{m}}^{-1}$
3. CThe second virial coefficient $B=(dZ/dP)RT$ is about $-49\mathrm{mL}\mathrm{mo}{\mathrm{l}}^{-1}$
4. DDoubling the pressure doubles the molar volume