Compute the average angular acceleration and the angular displacement during the 2 seconds a rotating object speeds up from 0.5 rad/s to 0.7 rad/s. 
选项为:A:a = 0.1 rad/s\textsuperscript{2}~$\Delta\theta$~= 0.3 radians  B:a = 0.2 rad/s\textsuperscript{2~}$\Delta\theta$~= 0.5 radians  C:a = 0.1 rad/s\textsuperscript{2~}$\Delta\theta$~= 1.2 radians  D:a = 0.2 rad/s\textsuperscript{2~}$\Delta\theta$~= 1.2 radians  请回答其中一个选项.