At a launch angle of 45°, the range of a launched projectile is given by 
选项为:A:$\dfrac{v\_{i}^{2}}{g}$  B:$\dfrac{2v\_{i}^{2}}{g}$  C:$\dfrac{v\_{i}^{2}}{2g}$  D:$\sqrt{\dfrac{v\_{i}^{2}}{2g}}$  请回答其中一个选项.