Four particles have speed 2, 3, 4 and 5 cm/sec respectively. Their RMS speed is

(A) 3.5 cm/sec

(B) ( 27 / 2 ) cm/sec

(C) ( $\sqrt{45}$ / 2 ) cm/sec

(D) ( $\sqrt{54}$ / 2 ) cm/sec

(A) 3.5 cm/sec

(B) ( 27 / 2 ) cm/sec

(C) ( $\sqrt{45}$ / 2 ) cm/sec

(D) ( $\sqrt{54}$ / 2 ) cm/sec