阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。
A
lf you are longing for a hike in Alaska and aren't sure where to start，here are our favorites. There's something for all levels of skills and ambitions.
The Kenai River Trail
A half mile down this trail are wonderful views of the Kenai River Canyon. There are really two trailheads(小道的起点); the main“upper" trail starts at mile 0.6 of Skilak Lake Rd，and the other at mile 2.3.
Turnagain Arm Trail
This 11-mile hike begins at Potter Trailhead (Mile 115). Initially used by AlaskaNatives, the trail，can also be accessible to points along the way: McHugh Creck(Mile 112)，Rainbow(Mile 108) and Windy(Mile 107).
lditarod National Historic Trail
The National Historic Iditarod Trail is a 24-mile hike used by gold miners and sled-dog teams until 1918，when the Alaska Railroad was finished. It's a two-to-three day hike through superb mountain scenery to Girdwood( where it's known as the Crow Pass Trail)，and is the region's best backpack adventure.
put up a tent at Echo Bend(Mile 3), or rent one of two yurts(毡房)($65 per night) close by. For a shorter outing you can turn around at the Perch，then return to the Dew Mound Trail at Echo Bend and then to the Nature Center，making this a scenic 8-mile trip.
Reed Lakes Trail
Two alpine lakes，waterfalls，glaciers and towering granite(花岗岩) walls: the7-to-9-mile Reed Lakes Trail is one of the most wonderful hikes in the region, and worth the climb. Once you reach upper Reed Lake，continue 1 mile to Bomber Glacier，where the ruin of a B-29 bomber lies in memorial to six men who died in a 1957 crash.
21. Which of the following was originally used by Alaska Natives?
A. The Kenai River Trail.
B. Turnagain Arm Trail.
C. Iditarod National Historic Trail.
D. Reed Lakes Trail.
22. At which place can hikers set up a tent?
A. Girdwood.
B. Potter Trailhead.
C. Echo Bend.
D. Turnagain Arm.
23. What will visitors see at Bomber Glacier?
A.A memorial to six heroes.
B. A tower made of granite.
c. The ruin of a B-29 bomber.
D. One of the most splendid waterfalls.
