In cold countries, water pipes sometimes burst, because

Large fresh water reservoir is fitted with two types of feeder pipes- hot water pipes and cold water pipes. Six cold water pipes alone can fill the reservoir in 12 hours. 3 cold water pipes and 9 hot water pipes together can fill the reservoir in 8 hours. How long will 5 hot water pipes alone take to fill the reservoir? 18 h r s 36 m in b. 20 h r s 45 m in c. 21 h r s 36 m in d. none of these

In cold countries, the phenomenon of looming takes place, because refractive index of air decreases with height