[单选题]
18.49: A particle has a totatm.-x*g fzu r+l energy of 500 MeV and a liuoaf 5v g 7wcl/5 55q:.xgq2 7mganpv *4igfzznear momentum of 300 $\frac{MeV}{c}$. What is the mass of the particle?
A. 800$\frac{MeV}{c^2}$
B. 583$\frac{MeV}{c^2}$
C. 400$\frac{MeV}{c^2}$
D. 267$\frac{MeV}{c^2}$
E. 200$\frac{MeV}{c^2}$
