15．It may seem strange that ice itself sometimes can protect crops from frost （霜冻）!Some growers actually spray their crops with water on a freezing night．Water freezes quickly on the plants and then a strange thing happens．As long as ice stays wet，it can't get colder than 0℃，a temperature many plants can stand．If the ice ever became entirely frozen and dry，it might drop many degrees lower，ruining （毁坏） the plants．But continually spraying water on the ice，the growers keep it from going below 0°C even if the air is much colder．This may be unbelievable but it saves the plants．
This strange kind of"ice blanket"works only on plants that are strong enough to stand the weight of frozen spray．The system is used even to protect banana plants on some Central American plantations．
36．As used in this passage，"ice blanket"meansC
A．a cold blanket B．a spray of frost
C．a covering of ice D．a warm blanket
37．This passage is intendedD．
A．to explain why some plants can withstand （耐） ice
B．to show how ice forms
C．to show that frost can be prevented
D．to give tips（窍门） on preserving （保护） crops
38．It can be concluded from the passage that ice would not protectC from frost．
A．banana trees
B．pine trees
C．tender rose bushes
D．apple orchards （果园）
39．The best title would beB．
A．Frost Triumphs Again
B．Ice Can be Nice
C．Battle of the Farmer
D．The Helpless Plant．
