[单选题]
A boat can move at 30 km/h i( um7/r ql5)dvfv,dpy;d: rlmn still w 6fb)i .om s/0/6cgzomt lib+later. How long will it take to move 12 km upstream in a river flowing . +)l/li zimgfbco66o/mbt 0s 6.0 km/h?
A. $20 \; min$
B. $22 \; min$
C. $24 \; min$
D. $30 \; min$
