[单选题]
A boat can move at 30 km/h in stilw+ ps*gw8f 2uiy-yi+ nl wat,.f4bc j54qxcvpikoo s1zt* 1er. How long will it take to move 12 km upstream in a river flowing 6.0 km/hvzx*ck1.4sbifq o1o, 54jtcp?
A. $20 \; min$
B. $22 \; min$
C. $24 \; min$
D. $30 \; min$
