Hot water cools from \[60{}^\circ C\]to \[50{}^\circ C\]in the first 10 minutes and to \[42{}^\circ C\] in the next 10 minutes. The temperature of the surrounding is

• A. \[5{}^\circ C\]              
• B. \[10{}^\circ C\]
• C. \[15{}^\circ C~~~~\] 
• D. \[20{}^\circ C\]