In a series LCR circuit, resistance $\mathrm{R}=10 \mathrm{\Omega }$  and the impedance $\mathrm{Z}=20 \mathrm{\Omega }.$ The phase difference between the current and the voltage is 

• A

  ${30}^{\mathrm{o}}$

• B

  ${45}^{\mathrm{o}}$

• C

  ${60}^{\mathrm{o}}$

• D

  ${90}^{\mathrm{o}}$