Off-season means good deals on flights, hotels and tours. You may also find that the locals are a bit friendlier and more welcoming when tourists aren't arriving in crowds.

　　In the winter months, there are less than seven hours of daylight; thus, chances are that you'll catch sight of the northern lights. Sunsets are also beautiful at this time, making for some great photo opportunities.

　　In Iceland, winter is the perfect time to hike glaciers, go ice climbing, explore caves made out of hardened lava(岩浆) and much more. One of the most popular activities is off-roading(越野比赛) in a specially-equipped "super jeep".

　　Before booking your trip, be sure to check for volcano alerts. There are about 130 volcanoes on or around Iceland. Thirty-five of them are active. In 2010, a volcano named Eyjaallajokull exploded, sending clouds of ash up to four kilometers into the atmosphere. The ash drifted toward the UK and Europe. Because the ash could damage aircraft engines, airlines operating in the region were forced to cancel flights for six days. As a result, thousands of people were stuck in airports.

　　Recently, another volcano named Bardarbunga has become active, erupting(喷发) ash into the air. Such events, if large enough, could prevent your trip from going ahead. So check the latest volcano news prior to（先于） making your reservations.

21. According to this article, why are you more likely to see the northern lights in the winter?

A. They move from rural areas to cities. B. The weather is less changeable at that time.

C. They're a special feature of many festivals. D. The sky is dark for longer periods then.

22. According to the article, how do visitors to Iceland have fun in the winter?

A. They learn how to ski down the mountains.

B. They photograph famous historic sites.

C. They explore the countryside in well made vehicles.

D. They spend a week at one of the seaside resorts.

23. What is true about the volcanoes of Iceland?