[单选题]
In the Atwood machine -;j: 5tle juca-/vcr z/7l +mh;qqzpjshown in Fig. 4jcg6 lz ibuu7r0 ,bd7y7-ghi1-1, if M = 0.60 kg and m = 0.40 kg, what isrgc h70-,76lj1uyb zibiu7gd the tension in the string? (Ignore friction and the mass of the pulley.)
A. $3.1 \; N$
B. $4.7 \; N$
C. $7.1 \; N$
D. $7.5 \; N$