[单选题]
Your motorboat can me7dd: vvedgee ,53yz) o a9aa8zh xqugdh kis7qq54v,k ;f2p 37ve at 30 km/h in still water. How much time will it take y;, vaqq igp 4a7ushz af3q9dkk7x8 52hou to move 12 km downstream, in a river flowing at 6.0 km/h?
A. $20 \; min$
B. $22 \; min$
C. $24 \; min$
D. $30 \; min$
