[单选题]
In the Atwood machine 5;uaogu+2 z:krr6 filkx6h* w shown in Fig. 4-1, if M = 0.60 kg and m = 0.40 kg9zp15 p4* nv f,s9wiixily*dl, what is the magnitude of the acceleration of the system? (Ignore friction and the fydvixl*l 9w, iizp4*9s1 pn5 mass of the pulley.)
A. $5.3 \; m/s^2$
B. $3.9 \; m/s^2$
C. $2.0 \; m/s^2$
D. $0.98 \; m/s^2$