[单选题]
In the Atwood machine s.21vrqrtgk 4rf2- i- iurqg;g hown in Fig. 4-1, if M = 0.60i jvi5nf k;)ec;-ua ,mqqed7 5 kg and m = 0.40 kg, what is the magni) mdue-;5nic57kje qfi;a,v qtude of the acceleration of the system? (Ignore friction and the mass of the pulley.)
A. $5.3 \; m/s^2$
B. $3.9 \; m/s^2$
C. $2.0 \; m/s^2$
D. $0.98 \; m/s^2$