[单选题]
At what temperature is the average kinetic energy of a9jcdv5yqn( k7 n atomdy)6pxc;oleny 8;;9pr jx: daq bh53x in helium gas equal topoq56c r; b)xh 9ne;8yd:;3lxxja dpy $6.21 \times 10^{-21} \; J$?
A. $200 \; K$
B. $250 \; K$
C. $300 \; K$
D. $350 \; K$
